Sustainability, Eco-Point and Engineering Performance of Different Workability OPC Fly-Ash Mortar Mixes

This study investigates the engineering performance and CO2 footprint of mortar mixers by replacing Portland cement with 10%, 20%, 40% and 60% fly ash, a common industrial waste material. Samples of self-compacting mortar (SCM) were prepared with four different water/binder ratios and varying dosages of superplasticizer to give three ranges of workability, i.e., normal, high and self-compacting mortar mix. The engineering performance was assessed in term of compressive strength after designated curing periods for all mixes. CO2 footprint was the environmental impact indicator of each production stage. The optimum mix obtained was at 10% replacement rate for all mixes. Total production emission reduced by 56% when the fly ash replacement rate increased from 0% to 60% (maximum). This is translated to a reduction of 80% in eco-points (assuming that the energy consumption rate of production with 0% fly ash is at 100%). Such re-utilization is encouraged since it is able to reduce possible soil toxicity due to sulfur leaching by 5% to 27% and landfill area by 15% to 91% on average.


Introduction
Self-compacting mortar (SCM) is an integral part of a self-compacting concrete (SCC) design, a technological evolution of the conventional concrete that does not require any vibrator for compaction. The self-compacting ability of fresh concrete enables it to fill formwork and encapsulate reinforcing bars through the action of gravity while maintaining homogeneity [1]. According to The International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM) [1], the self-compaction improves productivity and the condition of the working environment, as well as enhances the homogeneity of the mixes. The quality of SCC is controlled by three properties-flowing ability, passing ability and resistance to segregation. Flowing ability is the ability to fill the formwork. Having sufficient passing ability allows the mortar to pass through congested reinforcement without any separation or blocking. Lastly, resistance to segregation controls the retaining of coarse components of the mixes to maintain a homogenous state [2,3]. Self-compacting concrete can be used in most applications where normal concrete is commonly used. Nevertheless, its superior performance is more obvious in densely-reinforced structures, though less demanding applications, like backfill, are equally possible. SCC can be fiber reinforced and can be used in both in situ construction and pre-cast concrete [1].
In addition, a higher content of fine particles and well-graded aggregate tends to improve the flowability and stability of SCC and SCM [4]. SCC loaded with well-graded aggregates and fine cement produces a dense interfacial transition zone between the aggregate and the cement matrix, which enhances concrete strength and durability [2]. The ability to self-compact has made SCC an attractive choice internationally, but its higher manufacturing cost than conventional concrete has hindered its application in general construction.
Mortars with different binder types have been used since ancient times for different purposes [5]. SCM is preferred due to its ease of mixing while having excellent flowing ability [6]. This reduces casting costs and, again, produces a more homogeneous product. Many studies have been done on SCM [6][7][8][9][10][11][12][13], some focusing on lowering the production cost [14].
The technology may also convert a variety of waste materials into useful by-products as a method to reduce greenhouse gas emissions while solving the problem of the high disposal cost of waste materials, such as fly ash. Notable recent research incorporating fly ash as mineral admixtures, particularly in the SCC, include Bentz et al. [15], Dehwah [16], Gesoǧlu et al. [17], Bouzoubaa et al. [18] Sabet et al. [19] and Siddique [20]. Some researchers have also attempted to measure the CO 2 footprint in concrete. Putri et al. [21] studied the effect of fly-ash on the environmental sustainability and engineering performance of OPC-mortar. Flower et al. [22] reported the quantification of CO 2 emissions associated with the manufacture and placement of concrete in the Australian context; the life cycle inventory data were gathered from quarries, batching plants and a few other known sources. Equivalent CO 2 emissions were presented as the final result, and the potential of fly ash and ground granulated blast furnace slag (GGBS) to reduce the emissions was also investigated and presented. Yang et al. [23] proposed an evaluation procedure from cradle to pre-construction by using an individual integration that included the material, production, curing and transportation phases for estimating CO 2 reduction in alkali-activated concrete (AAC). The performance efficiency indicators for the binder were also determined for different types of concrete. In their findings, the reduction rate of CO 2 emission of AAC relative to Ordinary Portland Cement (OPC) concrete ranged between 55% and 75%. Cyr et al. [24] published an article concerning the design of eco-efficient grouts intended for soil nailing.
The utilization of waste material in cement mortar promotes green technology. Waste materials, such as fly ash, that are deposited into landfills without further consumption consume more space than necessary, not mentioning that they bring adverse environmental impacts, such as leaching and groundwater contamination. As such, green technologies become essential and should be promoted, such as the SCC. This technology, pioneered by Japan, has become the center of attention in recycling fly ash to lessen the CO 2 footprint. The CO 2 footprint of mortar production was thus measured in this study, as well as its effects on engineering performance and environmental sustainability. In fact, several authors [25][26][27][28][29] have attempted to relate environmental sustainability from other aspects by utilizing waste materials as supplementary cementing materials where the zero burden hypotheses (co-combustion of fly ashes) were implemented.

Experimental Program
The mix proportion of the mortar mixes is shown in Tables 1 and 2. Four different water/binder ratios (0.35, 0.40, 0.45 and 0.50), one control and four replacement levels of fly ash (10%, 20%, 40% and 60%) by weight of cement were adopted for this study. The superplasticizer dosage was determined earlier from the trial mixes to give three ranges of workability, which were normal slump flow (targeted at ď100 mm), high slump flow (targeted at 150-170 mm) and self-compacting flow (targeted at 240-260 mm). Sixty mortar mixes were prepared to determine the effect of different superplasticizer dosage on the flowability of mortar. This study used an ordinary Portland cement produced from the northern part of Peninsular Malaysia that conforms to the ASTM Type I standard. The silica sand was produced by a local mineral quarry, and the sizes used were 8/16 (1.2-2.4 mm), 16/30 (0.6-1.2 mm), 30/60 (0.3-0.6 mm) and 50/100 (0.3-0.075 mm). A sieve analysis was carried out to ascertaining the fineness modulus of the silica sand used, which was recorded at 2.58 and with a specific gravity of 2.64. The grading of silica sand was based on BS 882 [30], as shown in Figure 1. The Class F fly ash mineral admixture was obtained locally from a power station located in the northern part of Peninsular Malaysia. The cement and fly ash were analyzed using X-ray fluorescence (XRF) for chemical compositions, and the results together with the physical properties are presented in Table 3. In this present study, the tap water used was checked for any visible contaminants before mixing. The chemical admixture utilized was a modified poly-carboxylate superplasticizer admixture, which had a specific gravity of 1.08.

Specimen Preparation
The test specimens were prepared using a standard steel cube mold of 50 mm × 50 mm × 50 mm in dimensions. Sixty mortar cubes were cast for each mortar mix, giving a total of 1800 test cubes. Prior to casting, the cube molds were cleaned with a soft brush, and a thin layer of oil was applied to facilitate the removal of hardened concrete cube thereafter. A mini slump flow test and mini V-funnel test were conducted to assess the workability of the fresh mortar. Specimens were then cast in the molds, and only the normal and high slump flow mixes were compacted by tamping 25 times uniformly over the cross-section with a steel rod, as specified by ASTM C143/C143M [31]. The mortar specimens were kept covered and cured in the molds for 24 h, after which they were removed from the molds and placed in a curing tank at 20-21 °C, as specified by ASTM C511 [32]. The Class F fly ash mineral admixture was obtained locally from a power station located in the northern part of Peninsular Malaysia. The cement and fly ash were analyzed using X-ray fluorescence (XRF) for chemical compositions, and the results together with the physical properties are presented in Table 3. In this present study, the tap water used was checked for any visible contaminants before mixing. The chemical admixture utilized was a modified poly-carboxylate superplasticizer admixture, which had a specific gravity of 1.08.

Specimen Preparation
The test specimens were prepared using a standard steel cube mold of 50 mmˆ50 mmˆ50 mm in dimensions. Sixty mortar cubes were cast for each mortar mix, giving a total of 1800 test cubes. Prior to casting, the cube molds were cleaned with a soft brush, and a thin layer of oil was applied to facilitate the removal of hardened concrete cube thereafter. A mini slump flow test and mini V-funnel test were conducted to assess the workability of the fresh mortar. Specimens were then cast in the molds, and only the normal and high slump flow mixes were compacted by tamping 25 times uniformly over the cross-section with a steel rod, as specified by ASTM C143/C143M [31]. The mortar specimens were kept covered and cured in the molds for 24 h, after which they were removed from the molds and placed in a curing tank at 20-21˝C, as specified by ASTM C511 [32].

Sample Characterization
The samples were characterized into three different degrees of workability, namely normal flow (targeted at a slump flow diameter of 10-20 mm), high flow (targeted at a slump flow diameter of 150-170 mm) and a designed slump flow diameter range of 240-260 mm specifically for SCM. The targeted flowability was achieved by adjusting the dosage of the modified poly-carboxylate superplasticizer admixture used. The mortar samples were then tested to study the engineering properties, compressive strength and water absorption.
The compressive loading tests were carried out on a compression testing machine of a 500-kN capacity and a loading rate of 0.9 kN/s. The cube specimens measured 50 mmˆ50 mmˆ50 mm, and the experiment was repeated five times for every mix design before an average was taken for the highest three readings. The test was performed after 3, 7, 14, 28 and 90 days of curing in accordance with ASTM C109M [33]; results are shown in Appendices A-D. The specimens were tested immediately after being taken out of the curing tank.
A water absorption test was conducted when the mortar cubes reached the age of 28 days in accordance with British Standard (BS 1881: Part 122) [34]. Five mortar samples measuring 50 mmˆ50 mmˆ50 mm were oven-dried at 105˘5˝C for 72˘2 h undisturbed, but with only free-flowing air to all surfaces of the samples. The specimens were then cooled for 24˘0.5 h in a dry airtight vessel. Each specimen was then weighed and immediately immersed in a tank containing clean water maintained at 20˘1˝C and with a depth of 25˘1 mm over the top of the specimen. The samples were left for 30˘0.5 min, wiped dry and weighed again. The absorption rate of these samples was taken as the increase in weight after immersion and presented as the percentage of dry mass.

Slump Flow
As mentioned earlier, the ability and efficiency of self-compaction is measured through flowability, passing ability and also resistance to segregation. In this study, a mini slump flow test was carried out to check that each particular test mix had achieved the targeted flowability. This range has been previously used byŞahmaran et al, Khaleel et al. and Turk et al. [12,35,36]. Figures 2-4 show the dosage of superplasticizer for the targeted slump flow. Generally, the flowability of the mixes had improved with the incorporation of fly ash, possibly due to the round and spherical shape of the particles that had enhanced the rolling capability and the lubrication between particles.

Sample Characterization
The samples were characterized into three different degrees of workability, namely normal flow (targeted at a slump flow diameter of 10-20 mm), high flow (targeted at a slump flow diameter of 150-170 mm) and a designed slump flow diameter range of 240-260 mm specifically for SCM. The targeted flowability was achieved by adjusting the dosage of the modified poly-carboxylate superplasticizer admixture used. The mortar samples were then tested to study the engineering properties, compressive strength and water absorption.
The compressive loading tests were carried out on a compression testing machine of a 500-kN capacity and a loading rate of 0.9 kN/s. The cube specimens measured 50 mm × 50 mm × 50 mm, and the experiment was repeated five times for every mix design before an average was taken for the highest three readings. The test was performed after 3, 7, 14, 28 and 90 days of curing in accordance with ASTM C109M [33]; results are shown in Appendices A-D. The specimens were tested immediately after being taken out of the curing tank.
A water absorption test was conducted when the mortar cubes reached the age of 28 days in accordance with British Standard (BS 1881: Part 122) [34]. Five mortar samples measuring 50 mm × 50 mm × 50 mm were oven-dried at 105 ± 5 °C for 72 ± 2 h undisturbed, but with only free-flowing air to all surfaces of the samples. The specimens were then cooled for 24 ± 0.5 h in a dry airtight vessel. Each specimen was then weighed and immediately immersed in a tank containing clean water maintained at 20 ± 1 °C and with a depth of 25 ± 1 mm over the top of the specimen. The samples were left for 30 ± 0.5 min, wiped dry and weighed again. The absorption rate of these samples was taken as the increase in weight after immersion and presented as the percentage of dry mass.

Slump Flow
As mentioned earlier, the ability and efficiency of self-compaction is measured through flowability, passing ability and also resistance to segregation. In this study, a mini slump flow test was carried out to check that each particular test mix had achieved the targeted flowability. This range has been previously used by Şahmaran et al, Khaleel et al. and Turk et al. [12,35,36].     The fineness of powdered materials, such as fly ash, is highly beneficial in improving the workability of mixes and reducing bleeding effects. Fly ash also gives the mixes better cohesiveness and plasticity. Here, the superplasticizer (SP) dosage was the only dependent variable that would affect the targeted slump flow. The conclusion drawn was that the SP dosage utilized is highly dependent on the percentage of fly ash replacement level and workability. By increasing the fly ash replacement level, the workability generally improves, particularly for normal mixes. Figure 2 also shows that increasing the fly ash level has enhanced the workability, although a lower SP dosage would have been sufficient to achieve the targeted slump. A published study has mentioned that the mortar flowing ability decreased with higher SP dosages. The finding of this study is that the flowing ability can be increased with a higher SP dosage, provided that is at a lower water-binder ratio [6].
For control mixes without any fly ash added, the highest SP dosage was recorded at 1.0%. At the maximum fly ash replacement level of 60%, the lowest SP dosages were at 0.14%, 0.28% and 0.56%. This increase in SP dosage is due to the combined effect of greater paste volume and reduced fine material content that has decreased the flowing resistance of the mortar. A similar trend was noticed for water to binder (w/b) ratios of 0.40, 0.45 and 0.50. However, for 60% fly ash replacement, the SP dosage needed to be reduced significantly, and this was the same for every mix irrespective of    The fineness of powdered materials, such as fly ash, is highly beneficial in improving the workability of mixes and reducing bleeding effects. Fly ash also gives the mixes better cohesiveness and plasticity. Here, the superplasticizer (SP) dosage was the only dependent variable that would affect the targeted slump flow. The conclusion drawn was that the SP dosage utilized is highly dependent on the percentage of fly ash replacement level and workability. By increasing the fly ash replacement level, the workability generally improves, particularly for normal mixes. Figure 2 also shows that increasing the fly ash level has enhanced the workability, although a lower SP dosage would have been sufficient to achieve the targeted slump. A published study has mentioned that the mortar flowing ability decreased with higher SP dosages. The finding of this study is that the flowing ability can be increased with a higher SP dosage, provided that is at a lower water-binder ratio [6].
For control mixes without any fly ash added, the highest SP dosage was recorded at 1.0%. At the maximum fly ash replacement level of 60%, the lowest SP dosages were at 0.14%, 0.28% and 0.56%. This increase in SP dosage is due to the combined effect of greater paste volume and reduced fine material content that has decreased the flowing resistance of the mortar. A similar trend was noticed for water to binder (w/b) ratios of 0.40, 0.45 and 0.50. However, for 60% fly ash replacement, the SP dosage needed to be reduced significantly, and this was the same for every mix irrespective of  The fineness of powdered materials, such as fly ash, is highly beneficial in improving the workability of mixes and reducing bleeding effects. Fly ash also gives the mixes better cohesiveness and plasticity. Here, the superplasticizer (SP) dosage was the only dependent variable that would affect the targeted slump flow. The conclusion drawn was that the SP dosage utilized is highly dependent on the percentage of fly ash replacement level and workability. By increasing the fly ash replacement level, the workability generally improves, particularly for normal mixes. Figure 2 also shows that increasing the fly ash level has enhanced the workability, although a lower SP dosage would have been sufficient to achieve the targeted slump. A published study has mentioned that the mortar flowing ability decreased with higher SP dosages. The finding of this study is that the flowing ability can be increased with a higher SP dosage, provided that is at a lower water-binder ratio [6].
For control mixes without any fly ash added, the highest SP dosage was recorded at 1.0%. At the maximum fly ash replacement level of 60%, the lowest SP dosages were at 0.14%, 0.28% and 0.56%. This increase in SP dosage is due to the combined effect of greater paste volume and reduced fine material content that has decreased the flowing resistance of the mortar. A similar trend was noticed for water to binder (w/b) ratios of 0.40, 0.45 and 0.50. However, for 60% fly ash replacement, the SP dosage needed to be reduced significantly, and this was the same for every mix irrespective of the w/b ratio. This resulted in lower mortar density since the density of fly ash (2.27) is much lower compared to that of cement [25]. The significant relationship between slump flow and SP dosage is apparent, whereby increasing the SP dosage leads to greater flowability. Resistance of the fresh mortar to flow decreases in this case because of the liquefying action that consequently increases the flow spread of mortar. The overall results have also shown that the w/b ratio plays a vital role in this; an increase in the w/b ratio lowered the paste volume and increased the fine material content to produce a much lower flow spread.

V-Funnel
The V-funnel test assesses the viscosity, as well as the passing and filling ability of self-compacting concrete in particular [3]. It was carried out to ensure that the filling and passing ability is satisfactory. Resistance to segregation was assessed through visual observation during casting to ensure that the mixes are in a homogenous state. the w/b ratio. This resulted in lower mortar density since the density of fly ash (2.27) is much lower compared to that of cement [25]. The significant relationship between slump flow and SP dosage is apparent, whereby increasing the SP dosage leads to greater flowability. Resistance of the fresh mortar to flow decreases in this case because of the liquefying action that consequently increases the flow spread of mortar. The overall results have also shown that the w/b ratio plays a vital role in this; an increase in the w/b ratio lowered the paste volume and increased the fine material content to produce a much lower flow spread.

V-Funnel
The V-funnel test assesses the viscosity, as well as the passing and filling ability of self-compacting concrete in particular [3]. It was carried out to ensure that the filling and passing ability is satisfactory. Resistance to segregation was assessed through visual observation during casting to ensure that the mixes are in a homogenous state.    the w/b ratio. This resulted in lower mortar density since the density of fly ash (2.27) is much lower compared to that of cement [25]. The significant relationship between slump flow and SP dosage is apparent, whereby increasing the SP dosage leads to greater flowability. Resistance of the fresh mortar to flow decreases in this case because of the liquefying action that consequently increases the flow spread of mortar. The overall results have also shown that the w/b ratio plays a vital role in this; an increase in the w/b ratio lowered the paste volume and increased the fine material content to produce a much lower flow spread.

V-Funnel
The V-funnel test assesses the viscosity, as well as the passing and filling ability of self-compacting concrete in particular [3]. It was carried out to ensure that the filling and passing ability is satisfactory. Resistance to segregation was assessed through visual observation during casting to ensure that the mixes are in a homogenous state.    The addition of fly ash at replacement levels of 10%, 20%, 40% and 60% proportionally reduced the V-funnel time. The obvious reason is that the liquefying and dispersing actions of the SP decreased flow resistance. For control mixes at a lower w/b ratio, a large variation between V-funnel time and SP dosage was observed, while it was smaller for that with a higher w/b ratio. The mix proportions indicate that binder proportions are low with less water added into the mixes, which can be attributed to less SP present in the mixes. Figure 9 shows the relationship between the relative slump flow (Гm) and the relative funnel time speed (Rm). The results obtained are within the limits set by European Federation of National Assoctions Representing for Concrete (EFNARC) [3], which is a relative slump flow, (Гm) = 4.8, and relative funnel time speed, (Rm) = 1.2. Some data fell within the stipulated boundary belonged to the 60% fly ash replacement at higher w/b ratios of 0.45 and 0.5. Some previous studies had also reported similar trending of relative slump flow to relative V-funnel speed [12].  The addition of fly ash at replacement levels of 10%, 20%, 40% and 60% proportionally reduced the V-funnel time. The obvious reason is that the liquefying and dispersing actions of the SP decreased flow resistance. For control mixes at a lower w/b ratio, a large variation between V-funnel time and SP dosage was observed, while it was smaller for that with a higher w/b ratio. The mix proportions indicate that binder proportions are low with less water added into the mixes, which can be attributed to less SP present in the mixes. Figure 9 shows the relationship between the relative slump flow (Гm) and the relative funnel time speed (Rm). The results obtained are within the limits set by European Federation of National Assoctions Representing for Concrete (EFNARC) [3], which is a relative slump flow, (Гm) = 4.8, and relative funnel time speed, (Rm) = 1.2. Some data fell within the stipulated boundary belonged to the 60% fly ash replacement at higher w/b ratios of 0.45 and 0.5. Some previous studies had also reported similar trending of relative slump flow to relative V-funnel speed [12]. The addition of fly ash at replacement levels of 10%, 20%, 40% and 60% proportionally reduced the V-funnel time. The obvious reason is that the liquefying and dispersing actions of the SP decreased flow resistance. For control mixes at a lower w/b ratio, a large variation between V-funnel time and SP dosage was observed, while it was smaller for that with a higher w/b ratio. The mix proportions indicate that binder proportions are low with less water added into the mixes, which can be attributed to less SP present in the mixes. Figure 9 shows the relationship between the relative slump flow (Г m ) and the relative funnel time speed (R m ). The results obtained are within the limits set by European Federation of National Assoctions Representing for Concrete (EFNARC) [3], which is a relative slump flow, (Г m ) = 4.8, and relative funnel time speed, (R m ) = 1.2. Some data fell within the stipulated boundary belonged to the 60% fly ash replacement at higher w/b ratios of 0.45 and 0.5. Some previous studies had also reported similar trending of relative slump flow to relative V-funnel speed [12].

Environmental Sustainability Performance
The approach by Henry et al. [37] in calculating the CO2 footprint of concrete when using recycled aggregate has been adopted to understand the environmental sustainability performance of the self-compacting mortar mixes. CO₂ footprint was calculated based on the SCM mix proportions (kg/m 3 ) shown in Tables 1 and 2 and the CO2 emissions of concrete constituent in Malaysia (kg-CO2/tonne) shown in Table 4. The product of multiplication was adopted in the calculation of CO2 footprints by using data from the mix proportion and CO2 emission of concrete constituent [21]. The CO2 footprint of self-compacting mixes for each w/b ratio is presented in Figure 10. The reduction in CO₂ footprint was directly proportional to the reduction in the w/b ratio and the amount of fly ash replacement. When comparing the CO2 footprint to the control mixes, the benchmark set was that 100% of CO2 emission was assumed to have been released from the control mixes (100% of ordinary Portland cement gives 100% of CO2 release). Following this trend, at 10% fly ash replacement, it was found that 9.42% lesser CO2 had been released, followed by 20% of fly ash replacement at 18.85% and 40% of fly ash replacement at 37.69%. The reduction was highest at 60% of fly ash replacement, where a 56.54% decrease was recorded.
This positive observation shows that, by replacing fly ash to a maximum level of 60%, the CO₂ footprint can be significantly reduced by more than 50% "to reduce the CO2 emission in concrete mixes by minimizing the cement content, replacing it with other minerals" [38]. This will be highly beneficial in promoting environmental and economic sustainability. Table 5 shows overall comparison of CO2 emission from Malaysia, Japan, Australia, United Kingdom and South Africa presented by Putri et al. [21], Henry et al. [37], Flower et al. [22], The Concrete Centre [39] and Theodosiu [40], respectively. In this study, the CO2 footprint was calculated based on the SCM mix proportion (kg/m 3 ), as shown in Tables 1 and 2, while

Environmental Sustainability Performance
The approach by Henry et al. [37] in calculating the CO 2 footprint of concrete when using recycled aggregate has been adopted to understand the environmental sustainability performance of the self-compacting mortar mixes. CO 2 footprint was calculated based on the SCM mix proportions (kg/m 3 ) shown in Tables 1 and 2 and the CO 2 emissions of concrete constituent in Malaysia (kg-CO 2 /tonne) shown in Table 4. The product of multiplication was adopted in the calculation of CO 2 footprints by using data from the mix proportion and CO 2 emission of concrete constituent [21]. The CO 2 footprint of self-compacting mixes for each w/b ratio is presented in Figure 10. The reduction in CO 2 footprint was directly proportional to the reduction in the w/b ratio and the amount of fly ash replacement. When comparing the CO 2 footprint to the control mixes, the benchmark set was that 100% of CO 2 emission was assumed to have been released from the control mixes (100% of ordinary Portland cement gives 100% of CO 2 release). Following this trend, at 10% fly ash replacement, it was found that 9.42% lesser CO 2 had been released, followed by 20% of fly ash replacement at 18.85% and 40% of fly ash replacement at 37.69%. The reduction was highest at 60% of fly ash replacement, where a 56.54% decrease was recorded.
This positive observation shows that, by replacing fly ash to a maximum level of 60%, the CO 2 footprint can be significantly reduced by more than 50% "to reduce the CO 2 emission in concrete mixes by minimizing the cement content, replacing it with other minerals" [38]. This will be highly beneficial in promoting environmental and economic sustainability. Table 5 shows overall comparison of CO 2 emission from Malaysia, Japan, Australia, United Kingdom and South Africa presented by Putri et al. [21], Henry et al. [37], Flower et al. [22], The Concrete Centre [39] and Theodosiu [40], respectively. In this study, the CO 2 footprint was calculated based on the SCM mix proportion (kg/m 3 ), as shown in Tables 1 and 2 while CO 2 emissions of concrete constituent in Malaysia (kg-CO 2 /tonne) were determined as shown in Table 4. The differences in some data produced might be caused by the assumption of energy consumption made for each country with due inference made of the distance for transporting the materials [40]. emissions of concrete constituent in Malaysia (kg-CO2/tonne) were determined as shown in Table 4. The differences in some data produced might be caused by the assumption of energy consumption made for each country with due inference made of the distance for transporting the materials [40]. Kg-CO2/tonne Kg-CO2e/tonne GGBS and * are the notations for ground granulated blast slag and "not mentioned", respectively.

Compressive Strength versus Environmental Sustainability
This section shall discuss the relationship between compressive strength and CO2 footprint at 7, 28 and 90 days, interpreted through the plots of "n" day compressive strength against CO2 footprint. The produced mortar samples were found to have comparable workability after being cured for 7, 28 and 90 days in particular; the linearity of these plots produced the best-fit equations and coefficients of regression as shown in Figures 11-13, respectively. Linear equations established for each type of flow are summarized in Table 6 as follows.

Compressive Strength versus Environmental Sustainability
This section shall discuss the relationship between compressive strength and CO 2 footprint at 7, 28 and 90 days, interpreted through the plots of "n" day compressive strength against CO 2 footprint. The produced mortar samples were found to have comparable workability after being cured for 7, 28 and 90 days in particular; the linearity of these plots produced the best-fit equations and coefficients of regression as shown in Figures 11-13 respectively. Linear equations established for each type of flow are summarized in Table 6 as follows. high flow and SCM was 57.5, 65 and 70 MPa, respectively. The observed trend is that SCM had the largest increase in compressive strength through time. Furthermore, the coefficient of regression (R 2 ) established for 7, 28 and 90 days' strength to the CO2 footprint for each mix depicted a good correlation with an average of 0.873, 0.871 and 0.824, respectively. The linear equation established between 7, 28 and 90 days' compressive strength and CO2 footprint was only applicable for w/b ratios of 0.35-0.50 for all types of flow.

Determination of Optimum Mixes
The optimum mix for self-compacting mortar was determined based on the relationship between compressive strength and CO2 footprint, as shown in Figures 14-17 for w/b ratios of 0.35, 0.40, 0.45 and 0.50. The intersection point between these two variables was taken as the optimum mix.
Based on Figure 14 for a w/b ratio of 0.35, the optimum mix is when the replacement rate of cement with fly ash is 10%. A similar trend has been observed for all other w/b ratios and over 50% of the specimens, except for the w/b ratio of 0.5, which thus shows that a 10% replacement rate gives the best mix design for SCC. At w/b 0.50, the intersection fell on 20% fly ash replacement. The results The equations clearly showed that an increase in the line gradient has produced a much higher range of compressive strength for all mixes. A lower CO 2 footprint showed lower strength achieved and vice versa. Interestingly, self-compacting flow seems to give better strength, yet with a low CO 2 footprint. The strength at early age was an average of 39, 45 and 47.5 MPa for normal, high and self-compacting flow, respectively. At 28 days, these became an average of 50, 52.5 and 60 MPa, respectively. This continued to increase such that by the age of 90 days, the average for normal flow, high flow and SCM was 57.5, 65 and 70 MPa, respectively. The observed trend is that SCM had the largest increase in compressive strength through time. Furthermore, the coefficient of regression (R 2 ) established for 7, 28 and 90 days' strength to the CO 2 footprint for each mix depicted a good correlation with an average of 0.873, 0.871 and 0.824, respectively. The linear equation established between 7, 28 and 90 days' compressive strength and CO 2 footprint was only applicable for w/b ratios of 0.35-0.50 for all types of flow.

Determination of Optimum Mixes
The optimum mix for self-compacting mortar was determined based on the relationship between compressive strength and CO 2 footprint, as shown in Figures 14-17 for w/b ratios of 0.35, 0.40, 0.45 and 0.50. The intersection point between these two variables was taken as the optimum mix.
Based on Figure 14 for a w/b ratio of 0.35, the optimum mix is when the replacement rate of cement with fly ash is 10%. A similar trend has been observed for all other w/b ratios and over 50% of the specimens, except for the w/b ratio of 0.5, which thus shows that a 10% replacement rate gives the best mix design for SCC. At w/b 0.50, the intersection fell on 20% fly ash replacement. The results suggest that, rather than w/b ratio, the type of fly ash plays a more dominant role in affecting the strength and CO 2 footprint of the SCM mixes. In this study, a Class F fly ash (refer to Table 3) having low calcium oxide (CaO) and higher silicon dioxide (SiO 2 ) was used. Once the compressive strength and CO 2 footprint surpassed the optimum point, both started to decrease. At this point, the fly ash is only functioning as a filler material. Nevertheless, this also shows that, while the optimum replacement rate is at 10%, it can be increased up to 60% in spite of the recommended 40% or less by Khatib [41] to elevate the utilization rate of fly ash, and a high strength mortar can still be produced. Furthermore, this is highly possible if early strength is not an important factor [42]. In the study of Khatib [41], replacing 40% of ordinary Portland cement with fly ash had resulted in a higher strength of more than 65 N/mm 2 after 56 days of curing.

Durability versus Environmental Sustainability
Generally, the addition of fly ash decreased the water absorption and elevated the durability performance of the mortar samples. It has been reported that high quality mortar samples generally have a water absorption rate of less than 5% [43,44]. It appears that the water transportation for all mortar samples is affected by two factors-the pores of the cement paste and the interfacial transition zone (ITZ) between the cement paste and the aggregate [31]. It is noted that the volume of water absorption in the mortar specimens corresponds to the degree of porosity, which becomes higher in mortar added with fly ash compared to that without. The proportion of aggregate in the

Durability versus Environmental Sustainability
Generally, the addition of fly ash decreased the water absorption and elevated the durability performance of the mortar samples. It has been reported that high quality mortar samples generally have a water absorption rate of less than 5% [43,44]. It appears that the water transportation for all mortar samples is affected by two factors-the pores of the cement paste and the interfacial transition zone (ITZ) between the cement paste and the aggregate [31]. It is noted that the volume of water absorption in the mortar specimens corresponds to the degree of porosity, which becomes higher in mortar added with fly ash compared to that without. The proportion of aggregate in the mixture was designed to decrease as the w/b ratio decreases (see Tables 1 and 2). Therefore, the absolute value of the porosity in the specimens would decrease along with the w/b ratio.
Carbonation is the reaction of carbon dioxide in the environment with calcium hydroxide in cement paste with the presence of water. Since the carbonation reaction of mortar containing fly ash is low, this improves the durability of concrete, where it becomes denser and more resistant in an aggressive environment. Consequently, it reduces the corrosion rate and maintenance costs.
Water absorption is an indicator of durability, where lower water absorption indicates a low w/b ratio and better durability. In this study, the SCM with a high percentage of fly ash replacement gave the highest water absorption. This is attributed to the increase in paste volume due to the lower specific gravity of fly ash, which has enhanced the capillary pore volume and water absorption [45]. Figures 18 and 19 show the relationship between water absorption and the environmental sustainability impact in terms of CO 2 footprint for w/b ratios of 0.35, 0.40, 0.45 and 0.50 for all flow mixes. Generally, a positive linear relationship has been established for all cases.
In Figure 18, with the equations gathered, a lower absorption rate has been achieved with a similar CO 2 footprint value. The observation showed that the dominant factor in determining the relationship between durability and environmental sustainability is highly dependent on the w/b ratio rather than the type of flow. A low w/b ratio seems to provide better performance in terms of durability since it has fewer pores, specifically after adding the mineral admixture. Hence, from the analysis carried out, it can be concluded that SCM gave the lowest water absorption with the lowest CO 2 footprint.
The relationship between durability and environmental sustainability for w/b ratios of 0.45 and 0.50 produced a very similar trend, whereby a lower slope meant a lower absorption rate and CO 2 footprint (see Figure 19). All-in-all, there exists a strong correlation specifically for SCM between CO 2 footprint and water absorption. This also means that the correlation is also strong between the environmental sustainability and durability of concrete; with a low CO 2 footprint (less environmental impact), the water absorption becomes low, as well (low durability), and vice versa.
Carbonation is the reaction of carbon dioxide in the environment with calcium hydroxide in cement paste with the presence of water. Since the carbonation reaction of mortar containing fly ash is low, this improves the durability of concrete, where it becomes denser and more resistant in an aggressive environment. Consequently, it reduces the corrosion rate and maintenance costs.
Water absorption is an indicator of durability, where lower water absorption indicates a low w/b ratio and better durability. In this study, the SCM with a high percentage of fly ash replacement gave the highest water absorption. This is attributed to the increase in paste volume due to the lower specific gravity of fly ash, which has enhanced the capillary pore volume and water absorption [45]. Figures 18 and 19 show the relationship between water absorption and the environmental sustainability impact in terms of CO2 footprint for w/b ratios of 0. 35   In Figure 18, with the equations gathered, a lower absorption rate has been achieved with a similar CO2 footprint value. The observation showed that the dominant factor in determining the relationship between durability and environmental sustainability is highly dependent on the w/b ratio rather than the type of flow. A low w/b ratio seems to provide better performance in terms of durability since it has fewer pores, specifically after adding the mineral admixture. Hence, from the analysis carried out, it can be concluded that SCM gave the lowest water absorption with the lowest CO2 footprint.
The relationship between durability and environmental sustainability for w/b ratios of 0.45 and 0.50 produced a very similar trend, whereby a lower slope meant a lower absorption rate and CO2 footprint (see Figure 19). All-in-all, there exists a strong correlation specifically for SCM between CO2 footprint and water absorption. This also means that the correlation is also strong between the environmental sustainability and durability of concrete; with a low CO2 footprint (less environmental impact), the water absorption becomes low, as well (low durability), and vice versa.

Eco-Points of OPC-Fly Ash Self-Compacting Mortar Mixes
The reduction of greenhouse gases is a priority for all industries. Currently, the electrical power industry accounts for approximately 37% of the CO 2 emissions generated globally [46]. So far, relentless efforts have been poured into developing renewable energy, such as hydro power, solar power and wind power [47]. In this study, the CO 2 footprint was identified by capturing all constituents formed from cradle to gate production of the SCM, which includes transportation and energy (fuel, diesel and electricity) until the pre-construction stage [22]. The ecological value or eco-point is proposed to describe all associated processes that may incur CO 2 emission of OPC-fly ash in SCM mixes. These eco-points optimize the utilization of waste materials to mainly reduce Portland cement's consumption and also to decrease landfill disposal [48], which means the quantifying of CO 2 emission is mainly associated with the manufacture and placement of cement mortar, as well as the impact of landfill disposal. For now, the environmental impacts identified include consumption of non-renewable raw materials, energy sources and destruction of biodiversity. Not only that, since the cost of aggregates is very dependent on the transport distances, leading to extraction operations near construction sites, this multiplies the number of quarries and their biodiversity impacts. The evaluation of eco-points as suggested by Yang et al. [23] is described as follows: Eco´points " CO 2 footprint`Transportation`Energy pDiesel`Electricityq (1) Eco-points of w/b 0.35 for self-compacting mixes are tabulated in Tables 7-11. Tables 7-11 present the eco-point assessment for SCM from 0% up to 60% fly ash replacement. This assessment measures the carbon emission of three stages: the material and production of 1 m 3 of mortar; the distance required to transport the mortar; and the energy consumed (diesel oil and electricity) during production, transporting and batching the mixes. The sum of this is termed the "eco-point". Those for w/b 0.40, 0.45 and 0.50 are summarized graphically in Figure 20. Fundamentally, the trending has been the same for all w/b ratios where more energy is required when no fly ash is added, which in turn generated more eco-points. With this, it also indicates that, the higher the percentage of fly ash, the lesser the energy produced, because the fly ash particles have filled up the spaces and voids. In SCM, this is even more effortless, since no vibration is needed, thus requiring even lesser energy. Consequently, it decreases the eco-points and further lessens the CO 2 footprint. Results showed that total production emission reduced by 56% from 558.87 kg-CO 2 /FU down to 247.76 kg-CO 2 /FU when fly ash replacement rate increased from 0%-60% (maximum). This is translated to a reduction of 80% in eco-points (assuming that the energy consumption rate of production with 0% fly ash is at 100%). Therefore, this analysis has shown how the eco-points of any particular mix associated with fly ash replacement can achieve considerable savings associated with CO 2 emission.  [40], respectively; "." Denotes function of multiplications; **-not captured, since control is with 0% fly ash replacement.

Fly Ash Landfill
One of the major problems of all coal combustion power plants is the unused fly ash and bottom ash that bring environmental problems, such as air pollution and groundwater contamination, due to the leaching of metals from the ashes, especially the accumulation of the very fine particles of fly ash. The utilization of fly ash in replacing the cement in concrete mixture

Fly Ash Landfill
One of the major problems of all coal combustion power plants is the unused fly ash and bottom ash that bring environmental problems, such as air pollution and groundwater contamination, due to the leaching of metals from the ashes, especially the accumulation of the very fine particles of fly ash. The utilization of fly ash in replacing the cement in concrete mixture decreases both energy and CO 2 emitted during production [49]. In Malaysia, fly ash is an industrial waste material commonly deposited in landfills. This brings no benefits, but rather environmental nuisance [50]. Currently, 3.4-4 billion tonnes of municipal and industrial waste are generated annually, of which non-hazardous industrial waste accounts for 1.2 billion tonnes [51] and the amount of wastes dumped at landfills is radically increasing due to industrial development and urbanization. The production of fly ash in Malaysia is believed to be approaching two million tons annually [52]. Near zero utilization of such waste material occupies land and brings other problems, such as leaching of traceable and hazardous elements [53], as well as contamination of groundwater.
Due to its potential toxic elements (PTEs) production e.g., Cadmium (Cd), Chromium (Cr), Nickel (Ni), Lead (Pb) and organic compound e.g., polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) content, coal fly ash is classified as a scheduled and hazardous solid waste. Uncontrolled land disposal of coal fly ash is likely to cause unnecessary transformation in soil conditions, including contaminating the soil with PTEs, PAHs and PCBs. However, coal fly ash is also a valuable resource of important plant nutrients, e.g., Calcium (Ca), Magnesium (Mg), Pottasium (K), Phosphorus (P), Sulphur (S), Boron (B), Iron (Fe), Copper (Cu) and Zinc (Zn) [54], where the addition of 2%-5% of fly ash to calcareous soils has resulted in better plant growth compared to normal soils [55]. However, when the application exceeds 5%, the crop growth was significantly reduced [54]. Coal residues contain hazardous substances, which also pollute the environment if handled and disposed incorrectly.
The overall assessment was made by setting up distinct boundaries with due reference to the current practices in the industry. The fly ash was used directly from the power plant after the incineration process without any further processing stages. Considering the fact that fly ash is mostly exported to the cement producer before being dumped in the landfill, the boundaries for the assessment of fly ash landfill were limited to a smaller scale analysis. In addition, the fly ash used in the laboratory was obtained as a completely burned final by-product that could be used directly for concrete production without any further processing stages. Hence, it may positively have less impact on energy utilization.
A power plant in northern part of peninsular Malaysia produces ash at an average of 340,576 tonnes per month [56], and the production breakdown is as illustrated in Figure 21.
Generally, approximately 70% of it is sold to cement manufacturers and producers, while the remaining 30% is dumped to the ash pond due to quality control procedures [56]. Figure 22 shows the fly ash-sulfur content of ash produced from the power plant. Based on the data production, 1% fly ash has 0.08% of sulfur in the landfill itself [56]. This also means that, by reducing fly ash disposal at the landfill pond, a further 5%-27% reduction of sulfur content is possible. In addition, this also reduces the disposal area from 15%-91% on average per month (assuming 10%-60% of fly ash utilization in concrete or mortar mixes per month). However, whether or not the reduction in toxicity and occupied area has a significant impact on the environment and ecology has to be further investigated to cover a larger scale. a further 5%-27% reduction of sulfur content is possible. In addition, this also reduces the disposal area from 15%-91% on average per month (assuming 10%-60% of fly ash utilization in concrete or mortar mixes per month). However, whether or not the reduction in toxicity and occupied area has a significant impact on the environment and ecology has to be further investigated to cover a larger scale.  sulfur in the landfill itself [56]. This also means that, by reducing fly ash disposal at the landfill pond, a further 5%-27% reduction of sulfur content is possible. In addition, this also reduces the disposal area from 15%-91% on average per month (assuming 10%-60% of fly ash utilization in concrete or mortar mixes per month). However, whether or not the reduction in toxicity and occupied area has a significant impact on the environment and ecology has to be further investigated to cover a larger scale.

Fly Ash Contaminant Landfill Savings
Fly ash is primarily made up of silica, alumina and iron oxide and is no foreign in concrete and mortar mixes. Fly ash is produced from the combustion of coal production and is normally dumped in landfill ponds. The problem is that it may cause leaching of trace elements, such as zinc, lead, copper, chromium, cadmium, nickel and also mercury into the soil. Nevertheless, blending fly ash with lime can avoid water pollution if the fly ash is used as back-filling material under acid mine drainage conditions. The trace elements' concentrations are higher in acidic fly ash than alkaline fly ash. Table 12 summarizes several studies conducted by Bie et al. [57], Tsiridis et al. [58], Jala et al. [59], Tripathi et al. [60], Pandey et al. [61], Riehl et al. [62] and Pourrut et al. [63] in analyzing trace element in fly ash landfill soil. The standard measurement of contaminated soil reported by the Department of Environmental Malaysia [64] is also included in the analysis. Figure 23 shows the breakdown analysis of fly ash toxicity reduction in contaminated landfill soils. The trend is similar for 10%, 20%, 40% and 60% of fly ash replacement for all trace elements. The high level of zinc (Zn) may also be coming from the plants and due to soil weathering. Mercury (Hg) impact is negligible since the reduction in contamination is similar for 0%-60% fly ash replacement. From the analysis, it is clear that reducing the disposal of fly ash is highly beneficial to the environment. Fly ash is primarily made up of silica, alumina and iron oxide and is no foreign in concrete and mortar mixes. Fly ash is produced from the combustion of coal production and is normally dumped in landfill ponds. The problem is that it may cause leaching of trace elements, such as zinc, lead, copper, chromium, cadmium, nickel and also mercury into the soil. Nevertheless, blending fly ash with lime can avoid water pollution if the fly ash is used as back-filling material under acid mine drainage conditions. The trace elements' concentrations are higher in acidic fly ash than alkaline fly ash. Table 12 summarizes several studies conducted by Bie et al. [57], Tsiridis et al. [58], Jala et al. [59], Tripathi et al. [60], Pandey et al. [61], Riehl et al. [62] and Pourrut et al. [63] in analyzing trace element in fly ash landfill soil. The standard measurement of contaminated soil reported by the Department of Environmental Malaysia [64] is also included in the analysis. Figure 23 shows the breakdown analysis of fly ash toxicity reduction in contaminated landfill soils. The trend is similar for 10%, 20%, 40% and 60% of fly ash replacement for all trace elements. The high level of zinc (Zn) may also be coming from the plants and due to soil weathering. Mercury (Hg) impact is negligible since the reduction in contamination is similar for 0%-60% fly ash replacement. From the analysis, it is clear that reducing the disposal of fly ash is highly beneficial to the environment.

Conclusions
The CO2 footprint was correlated with the engineering properties of mortar for three different spread flows (normal, high and self-compacting). The experimental results clearly demonstrated that replacing cement with other materials can reduce the environmental impact due to the lower CO2 footprint. From the present experimental investigation and assessment of the environmental impact, the following conclusions can be drawn:

Conclusions
The CO 2 footprint was correlated with the engineering properties of mortar for three different spread flows (normal, high and self-compacting). The experimental results clearly demonstrated that replacing cement with other materials can reduce the environmental impact due to the lower CO 2 footprint. From the present experimental investigation and assessment of the environmental impact, the following conclusions can be drawn:

1.
Considering the strength of mortar and environmental sustainability, the optimum mix for self-compacting mortar is at a 10% replacement rate of cement with fly ash for all mixes.

2.
From the plots of CO 2 footprint against compressive strength at various ages, a 60% replacement of cement with fly ash had decreased more than 50% of the CO 2 footprint compared to other mixes.

3.
The analysis of 28 days' compressive strength to CO 2 footprint showed that, with the increase in strength, a linear relationship had been obtained for both variables.

4.
The analysis of environmental impact concluded that self-compacting flow gave the lowest water absorption and the lowest CO 2 footprint.
The utilization of fly ash in concrete or mortar can reduce sulfur content in the soil by 5%-27%. 7.
The occupied landfill area of fly ash can be reduced by 15%-91% on average.