Effects of Recycled and Supplemented Cementitious Materials on Corrosion Resistance and Mechanical Properties in Reinforced Concrete

Abstract

Reinforced concrete is the most widely utilized building material for bridges, buildings, and other infrastructure components, and its longevity is significantly influenced by corrosion or rust. Corrosion shortens reinforced concrete’s service life and safety, which raises maintenance expenses. Concrete is a porous material that allows air and water to pass through, and corrosion begins when the air and water reach the steel. This study evaluated the mechanical and corrosion resistance properties of reinforced concrete containing recycled and supplemented cementitious materials. The results showed that mixtures containing fine glass aggregate, glass powder, slag, fly ash, or silica fume significantly improved the compressive, tensile, and flexural strengths, but the 10% slag mix, and 5% glass aggregate with 10% glass powder with 10% fly ash mix produced the best results overall. In addition, the mixture containing 15% fly ash produced the best result against corrosion. The corrosion tests revealed that mixtures with 10% slag and 20% glass powder also significantly enhanced the corrosion resistance of steel with the same results, confirming their effectiveness in reducing the permeability and increasing the durability of reinforced concrete.

1. Introduction

Reinforced concrete is one of the most widely used structural materials in roads, buildings, bridges, and infrastructure around the world, due to its high strength and long-term durability. However, as with any material, reinforced concrete is exposed to environmental factors that may lead to the deterioration of its components, especially the steel, due to corrosion or rusting. This corrosion weakens the concrete structure, requiring frequent repair or even demolition and reconstruction in critical cases.

Concrete has been one of the most extensively used building materials in human history, from its simple beginnings in antiquity to becoming an essential part of contemporary infrastructure [1]. The continuous innovation in this field is demonstrated by the development of new varieties of concrete, such as high-performance concrete that can survive extreme environmental conditions and self-consolidating concrete that flows readily into forms without the need for vibration. Additionally, the emphasis on sustainability has boosted the usage of extra cementitious materials, such as slag and fly ash, which lower the carbon footprint associated with the manufacture of concrete [2].

Concrete is made from four primary materials: cement, which acts as the binding agent; water, which activates the cement through hydration; aggregates, including fine aggregates such as sand and coarse aggregates such as gravel or crushed stone, which provide bulk and strength; and admixtures, which are added to enhance specific properties such as strength, workability, permeability, durability, or setting time. Together, these materials create versatile and durable construction materials that are used worldwide [3,4].

There has been extensive research into avoiding corrosion in reinforced concrete, involving strategies aimed at enhancing concrete’s durability, improving the protection of the reinforcing elements, and developing materials or techniques that reduce the likelihood of corrosion. The following is an overview of key research areas and strategies developed to prevent reinforced concrete corrosion and enhance mechanical properties, which are also summarized in Table 1 (Literature Review).

High-performance concrete (HPC) is designed to have low permeability, which helps reduce the ingress of aggressive agents like chlorides, sulfates, and CO₂. HPC typically contains supplementary cementitious materials (SCMs) like fly ash, slag, and silica fume, which improve the microstructure of concrete, making it denser and more resistant to corrosion. Research has shown that HPC significantly delays the onset of corrosion in reinforced concrete structures, particularly in harsh environments [5].

Supplementary cementitious materials (SCMs) such as fly ash, slag, and silica fume are widely used to enhance concrete durability and reduce corrosion risk. These materials reduce the permeability of concrete and help in binding chlorides, thus preventing their penetration into the steel reinforcement. Numerous studies have confirmed that the incorporation of SCMs in concrete significantly increases its resistance to both chloride-induced and carbonation-induced corrosion. [6].

Several studies have explored the use of corrosion-resistant reinforcement materials to prevent concrete corrosion. This includes the use of stainless steel, epoxy-coated reinforcement, and galvanized steel. Stainless steel is highly resistant to both chloride-induced and carbonation-induced corrosion, while epoxy-coated steel provides a physical barrier that prevents the initiation of corrosion. Research has shown that these materials are highly effective in increasing the lifespan of reinforced concrete structures, especially in coastal and marine environments [7].

Surface treatments such as sealers, coatings, and membranes are commonly used to protect concrete from corrosion. These treatments form barriers on the surface of the concrete, preventing the ingress of water, chlorides, and carbon dioxide. Various research studies have explored the efficacy of different surface coatings, including silane, siloxane, and epoxy-based coatings, in prolonging the durability of concrete in aggressive environments [8].

Corrosion inhibitors are chemical compounds added to the concrete mix or applied on the surface to prevent or slow down the corrosion process. Commonly used inhibitors include calcium nitrite, sodium benzoate, and organic-based inhibitors. Research has shown that corrosion inhibitors play a crucial role in minimizing the corrosion rate, especially in structural applications exposed to chloride environments. Calcium nitrite, for example, works by enhancing the passivation layer around the steel reinforcement, thereby delaying the onset of corrosion [9].

Recent research on self-healing concrete has shown promise in preventing corrosion by automatically sealing cracks that form over time. Microcapsules containing healing agents (e.g., epoxy resins or calcium carbonate-producing bacteria) are embedded into the concrete. When cracks form, the microcapsules rupture and release the healing agents, sealing the cracks and preventing the ingress of water and corrosive agents. Studies have demonstrated the effectiveness of this technology in reducing the likelihood of corrosion in cracked concrete [10].

Maintaining a low water–cement (w/c) ratio is one of the simplest yet most effective strategies for avoiding concrete corrosion. A low w/c ratio results in a denser concrete matrix with fewer pores, which reduces the permeability and thus limits the ingress of water, chlorides, and other harmful agents. Research has shown that a lower w/c ratio enhances the durability of concrete and delays the initiation of corrosion in steel reinforcement [11].

Admixtures such as waterproofing agents, shrinkage reducers, and air-entraining agents have been widely used to improve concrete resistance to corrosion. These admixtures work by reducing the permeability of the concrete and preventing the ingress of moisture and harmful chemicals. Research has shown that the use of such admixtures, in combination with a low water-cement ratio and SCMs, significantly enhances the long-term durability of reinforced concrete [12].

Recent research has also explored the development of chloride diffusion barrier layers within concrete. This involves incorporating layers of low-permeability materials, such as pozzolans or nano-silica, into the concrete mix. These layers act as barriers to the diffusion of chloride ions, significantly reducing the likelihood of corrosion. This technique has been shown to be particularly effective in marine and coastal environments, where chloride exposure is a primary concern [13].

Many studies have found that combining different corrosion prevention techniques yields better results than relying on a single method. For example, using corrosion inhibitors in conjunction with low w/c ratio concrete, cathodic protection, and surface coatings can create a multi-layered defense system. Research has demonstrated that hybrid systems significantly extend the life of reinforced concrete structures, even in highly aggressive environments [14].

With the growing threat of climate change, researchers have focused on designing concrete mixtures that are resilient to extreme environmental conditions, such as increased temperatures, humidity, and higher CO₂ concentrations. These mixtures typically include SCMs, low w/c ratios, and advanced corrosion inhibitors that can withstand the accelerated aging caused by climate-related factors. Research indicates that climate-resilient concrete can significantly reduce the risk of corrosion in future infrastructure [15].

Nanotechnology has emerged as a promising field for enhancing the performance of concrete in terms of corrosion resistance. Researchers are investigating the incorporation of nano-silica, nano-titanium dioxide, and other nanomaterials in concrete mixes to improve its mechanical properties, reduce permeability, and increase resistance to corrosion. Nano-silica, in particular, helps refine the concrete microstructure, resulting in a denser matrix that limits the ingress of corrosive agents [16].

Fiber-reinforced polymers (FRPs) are increasingly being used to strengthen and protect concrete structures from corrosion. FRP materials are lightweight, non-corrosive, and have high tensile strength, making them ideal for wrapping concrete columns, beams, and decks to prevent moisture and chlorides from penetrating the structure. Research has shown that FRP systems can significantly enhance the durability of reinforced concrete in environments with high exposure to salt and moisture [17].

The alkali–aggregate reaction (AAR) is a chemical reaction between the alkalis in cement and reactive aggregates that cause concrete to expand and crack. This creates pathways for moisture and chlorides to penetrate concrete, leading to corrosion of the reinforcement. Research on mitigating AAR involves the use of low-alkali cement, SCMs like fly ash, and lithium-based admixtures to control the reaction and prevent corrosion [18].

Crystalline waterproofing admixtures are relatively new technologies used to enhance concrete resistance to water penetration and corrosion. These admixtures form insoluble crystals in the concrete’s pores, which block the ingress of water and harmful substances. Research indicates that crystalline waterproofing is effective in preventing water-induced corrosion in underground structures, basements, and marine environments [19].

Reducing the amount of clinker in cement by using SCMs such as fly ash or slag not only helps reduce the environmental footprint of concrete but also increases its resistance to corrosion. Low-clinker cements are less reactive to chlorides and CO₂, thus improving durability. Research has demonstrated that these low-clinker cement mixes have lower permeability and better long-term performance in preventing corrosion [20].

Geopolymer concrete is a sustainable alternative to traditional Portland cement concrete, made from industrial by-products such as fly ash or slag, activated by alkaline solutions. Research has shown that geopolymer concrete exhibits excellent resistance to corrosion, particularly in aggressive environments, due to its low permeability and high resistance to chemical attack. It also has a reduced carbon footprint compared to conventional concrete, making it an environmentally friendly solution [21].

The depth of concrete cover, which refers to the distance between the steel reinforcement and the outer surface of the concrete, plays a critical role in preventing corrosion. Research has demonstrated that increasing the concrete cover depth reduces the likelihood of aggressive agents like chlorides and CO₂ reaching the reinforcement, thus delaying the initiation of corrosion. A thicker cover also provides better protection against freeze–thaw cycles and sulfate attack [22].

Self-consolidating concrete (SCC) is designed to flow easily and fill formwork without the need for mechanical vibration. The use of SCC improves the consolidation of concrete around the reinforcement, minimizing voids and reducing the permeability of concrete. Research has shown that SCC has a lower risk of corrosion initiation due to its dense microstructure, making it suitable for structures where durability and longevity are critical [23].

Recent research has explored the use of hybrid organic–inorganic coatings as a means of protecting reinforced concrete structures from corrosion. These coatings combine the flexibility and adhesion of organic materials with the durability and chemical resistance of inorganic components. Studies have shown that these hybrid coatings provide excellent resistance to chloride ingress and carbonation, making them highly effective in aggressive environments such as marine and industrial areas [24].

Bio-based solutions for corrosion prevention have gained attention in recent years, particularly the use of bacteria and other microorganisms to protect concrete. For example, bacteria capable of precipitating calcium carbonate are introduced into concrete, where they can seal cracks and prevent the ingress of water and chlorides. Research has shown that bio-based solutions, such as bacteria-based self-healing concrete, can significantly enhance durability and reduce the risk of corrosion [25].

Khedr and Idriss examined the effectiveness of silica fume (SF) concrete in resisting damage caused by the corrosion of embedded steel reinforcement. They investigated how the addition of silica fumes improved the concrete’s durability and resistance to corrosive agents, such as chlorides and moisture, which caused the steel reinforcement to corrode and led to structural deterioration. Through experimental testing, they assessed the performance of silica fume concrete, showing how its reduced permeability and enhanced strength prolonged the lifespan of reinforced concrete structures [26].

Boga and Topçu investigated the influence of fly ash (FA) on the corrosion resistance and chloride ion permeability of concrete. Their experimental analysis explored how incorporating fly ash into concrete mixtures affected the material’s ability to resist corrosion by limiting the penetration of chloride ions, thus reducing the permeability and improving the durability of the material. Their findings demonstrated that the addition of fly ash could prolong the service life of reinforced concrete structures exposed to aggressive environments [27].

Jau and Tsay examined the basic engineering properties of slag cement concrete and its resistance to seawater corrosion. By analyzing key engineering properties such as strength, permeability, and resistance to chemical attack, the authors assessed how slag cement improved the concrete’s ability to withstand seawater-induced corrosion. Their findings highlight that slag cement concrete offered better long-term performance and resilience in coastal and marine structures by minimizing the deterioration due to chloride ingress and corrosion of steel reinforcement [28].

Some researchers have stated that the addition of recycled glass in various forms can improve the mechanical properties of concrete, whether glass powder (GP), glass aggregate (GA), or even glass fiber (GF). These provide higher resistance to corrosion and chemical attacks and have a positive effect on the durability of concrete without compromising its strength [29,30,31].

Other researchers also achieved satisfactory results. They tested different samples of normal concrete, adding different proportions of glass powder. The results showed a noticeable improvement in minimizing oxygen permeability, chloride diffusion, and concrete resistance to electricity [9,10].

In their experiments, Kim et al. showed that using glass powder along with fly ash could add benefits. After adding glass powder and fly ash in different quantities in several samples, the strength of the concrete increased, and the penetration of chloride ions decreased [32]. Liu et al. used certain proportions of glass aggregate (GA) in addition to fly ash as an alternative material to fine aggregate in the concrete. The results of their tests showed that this mixture achieve a relatively lower strength than conventional concrete, but it increased the resistance of reinforced concrete to corrosion and reduced the porosity [33]. Other Liu et al. also added that adding glass fiber to plastic fiber can give effective results in reducing the rate of chloride spread in concrete [34]. Generally, the focus of this work is corrosion resistance, as related to the mechanical properties of different mixtures of concrete.

Table 1. Summary of the mixture design results of the research from the literature review.

Type Of Admixture	%Admixture of Cement	%Water	%Cement	%Coarse Aggregates	%Fine Aggregates	%Admixture		7 Days (MPa)	28 Days (MPa)
Silica Fume, (SF) [26]	0	8.92	20.36	38.15	32.58	-	-	35.30	42.20
	10	8.92	18.32	38.15	32.58	2.04	-	34.30	46.10
	15	8.92	17.31	38.15	32.58	3.05	-	37.30	48.10
	20 *	8.92	16.29	38.15	32.58	4.07	-	44.60	54.90
	25	8.92	15.27	38.15	32.58	5.09	-	37.80	47.20
Fly Ash, (FA) [27]	0	6.19	12.37	44.95	36.49	-	-	-	36.00
	15 *	6.24	10.61	44.84	36.44	1.87	-	-	38.00
	30	6.29	8.81	44.78	36.34	3.78	-	-	33.00
	45	6.35	6.99	44.67	36.28	5.72	-	-	27.00
Slag [28]	0	10.23	21.31	41.81	26.65	-	-	49.03	51.48
	10 *	10.23	19.18	41.81	26.65	2.13	-	46.60	48.05
	20	10.23	17.05	41.81	26.65	4.26	-	44.12	46.6
	30	10.23	14.92	41.81	26.65	6.39	-	43.15	45.11
	50	10.23	10.66	41.81	26.65	10.66	-	36.77	40.21
Glass Powder, (GP) [30]	0	7.56	18.92	35.71	37.81	-	-	-	65.20
	20 *	7.56	15.13	35.71	37.81	3.79	-	-	62.50
	30	7.56	13.23	35.71	37.81	5.69	-	-	59.50
	40	7.56	11.34	35.71	37.81	7.58	-	-	46.40
Glass Powder (GP)/Fly Ash (FA) [32]	0/20	6.70	11.91	41.15	37.27	-	2.98	19	27.5
	10/10 *	6.66	13.33	40.23	36.44	1.67	1.67	27.00	33.50
	5/0	6.63	14.01	41.26	37.36	0.74	-	27.00	33.50
	10/0	6.64	13.29	41.24	37.35	1.48	-	24.00	30.00
Glass Aggregates (GA)/Fly Ash (FA) [33]	0	8.12	12.31	51.28	25.21	-	3.08	42.50	47.5
	0.5 *	8.10	12.27	51.13	17.60	7.84	3.07	37.50	44.00
	1	8.07	12.23	50.98	10.03	15.63	3.06	36.00	43.50
	1.5	8.04	12.18	50.76	-	25.97	3.05	35.00	41.50

* The bold rows show the maximum resistance to corrosion, which form the basis for this investigation.

Table 1. Summary of the mixture design results of the research from the literature review.

Type Of Admixture	%Admixture of Cement	%Water	%Cement	%Coarse Aggregates	%Fine Aggregates	%Admixture		7 Days (MPa)	28 Days (MPa)
Silica Fume, (SF) [26]	0	8.92	20.36	38.15	32.58	-	-	35.30	42.20
	10	8.92	18.32	38.15	32.58	2.04	-	34.30	46.10
	15	8.92	17.31	38.15	32.58	3.05	-	37.30	48.10
	20 *	8.92	16.29	38.15	32.58	4.07	-	44.60	54.90
	25	8.92	15.27	38.15	32.58	5.09	-	37.80	47.20
Fly Ash, (FA) [27]	0	6.19	12.37	44.95	36.49	-	-	-	36.00
	15 *	6.24	10.61	44.84	36.44	1.87	-	-	38.00
	30	6.29	8.81	44.78	36.34	3.78	-	-	33.00
	45	6.35	6.99	44.67	36.28	5.72	-	-	27.00
Slag [28]	0	10.23	21.31	41.81	26.65	-	-	49.03	51.48
	10 *	10.23	19.18	41.81	26.65	2.13	-	46.60	48.05
	20	10.23	17.05	41.81	26.65	4.26	-	44.12	46.6
	30	10.23	14.92	41.81	26.65	6.39	-	43.15	45.11
	50	10.23	10.66	41.81	26.65	10.66	-	36.77	40.21
Glass Powder, (GP) [30]	0	7.56	18.92	35.71	37.81	-	-	-	65.20
	20 *	7.56	15.13	35.71	37.81	3.79	-	-	62.50
	30	7.56	13.23	35.71	37.81	5.69	-	-	59.50
	40	7.56	11.34	35.71	37.81	7.58	-	-	46.40
Glass Powder (GP)/Fly Ash (FA) [32]	0/20	6.70	11.91	41.15	37.27	-	2.98	19	27.5
	10/10 *	6.66	13.33	40.23	36.44	1.67	1.67	27.00	33.50
	5/0	6.63	14.01	41.26	37.36	0.74	-	27.00	33.50
	10/0	6.64	13.29	41.24	37.35	1.48	-	24.00	30.00
Glass Aggregates (GA)/Fly Ash (FA) [33]	0	8.12	12.31	51.28	25.21	-	3.08	42.50	47.5
	0.5 *	8.10	12.27	51.13	17.60	7.84	3.07	37.50	44.00
	1	8.07	12.23	50.98	10.03	15.63	3.06	36.00	43.50
	1.5	8.04	12.18	50.76	-	25.97	3.05	35.00	41.50

* The bold rows show the maximum resistance to corrosion, which form the basis for this investigation.

2. Materials and Methods

Table 2. Chemical composition average of primary constituent for cement and admixtures [35,36,37].

Material (Type)	Chemical Composition (%)
	SiO2	Al2O3	CaO	Fe2O3
Cement (ordinary Portland cement, type-I)	21.10	5.37	63.65	3.14
Silica fume (SF) (by-product of silicon and ferrosilicon)	93.30	-	9.25	-
Fly ash (FA) (by-product of coal)	51.50	24.30	5.15	8.87
Slag (by-product of iron)	16.10	3.80	30.60	31.70
Glass powder or glass aggregate (GP or GA) (recycled glass waste)	67.50	11.30	9.25	0.23

and

Table 3. Summary of specimen ingredients.

Ingredients	%Coarse Aggregates	%Cement	%Sand	%Water	%Silica Fume	%Fly Ash	%Slag	%Glass Powder	%Glass Fin Aggregates
Standard	47.25	13.77	31.24	7.75	-	-	-	-	-
20% SF	47.25	11.02	31.24	7.75	2.75	-	-	-	-
15% FA	47.25	11.70	31.24	7.75	-	2.07	-	-	-
10% Slag	47.25	12.39	31.24	7.75	-	-	1.38	-	-
20% GP	47.25	11.02	31.24	7.75	-	-	-	2.75	-
10%GP + 10%FA	47.25	11.02	31.24	7.75	-	1.38	-	1.38	-
5%GA + 10%FA + 10%GP *	47.25	11.02	29.68	7.75	-	1.38	-	1.38	1.56

* New combination.

provide the main materials with their chemical compositions and a summary of the specimen ingredients (concrete mixtures) used in this study, respectively.

The tests in this study were diverse and distributed throughout the project’s various phases. Sieve analysis was the first material preparation phase for concrete mix preparation. This was followed by the remaining tests: compressive strength, tensile strength, flexural strength, and corrosion. These tests were applied to samples after 28 days in the water for the concrete curing phase. The tests were conducted in compliance with the relevant ASTM, as shown in

Table 4. Standards of tests according to ASTM.

Material Quality Tests	Equipment Used	ASTM
Sieve Analysis of Fine and Coarse Aggregates	Sieve Shaker	ASTM C136 [38]
Compressive Strength of Cylindrical Concrete Specimens “Applying a loading rate on the specimen within the range of 8.4 MPa/min to 20.4 MPa/min” *	Compression Test Machine	ASTM C39 [39]
Flexural Strength of Concrete “Applying a loading rate that constantly increases the extreme fiber stress between 0.86 MPa/min and 1.21 MPa/min” *	Third-point Loading Method	ASTM C78 [40]
Splitting Tensile Strength of Cylindrical Concrete Specimens “Applying constant loading rate within the range 0.689 MPa/min to 1.38 MPa/min” *	Compression Test Machine	ASTM C496 [41]
Corrosion Potentials of Uncoated Reinforcing Steel in Concrete (Half-Cell Potential Method)	High-impedance Voltmeter	ASTM C876 [42]

* Rate of loading until failure of the specimen.

.

Given the importance of the testing phase—which is considered one of the most important research phases due to its impact—three samples were designed for each test, and the average results were considered.

The sieve analysis of the aggregate was conducted according to ASTM C136 to determine the particle size distribution of coarse and fine aggregates (Figure 1), and the results were within the ASTM C33 standard (Figure 2 and Figure 3) [43].

Sieve analysis was also applied to the cement and glass powder to compare the fineness modulus of the two materials (Figure 4 and Figure 5). In this study, specifically in mixtures containing glass powder, a percentage of the cement was replaced by glass powder. Therefore, the fineness modulus was examined to raise the glass powder up to the fineness of cement, for replacement in the mixture. The glass powder was prepared by grinding the glass in a grinding machine in the laboratory (Figure 6). Several tests were conducted to achieve a fineness level close to that of cement; finally, grinding was adopted for 5 min at medium speed on the grinding machine. After testing the cement and glass powder and calculating the fineness modulus, satisfactory results were obtained, close to each other at 0.6571 and 0.9697, respectively. This enabled replacing a percentage of the cement with glass powder in the concrete mixtures. Furthermore, the fine glass aggregates were within the ASTM C33 limits, which was accomplished by removing a percentage of sand (Figure 7).

Fineness modulus of cement:

$$FM= {\displaystyle \frac{\sum Cumulative \% Retained on 5,2.36,1.18,0.6,0.3,0.15}{100}},$$

(1)

$$FM={\displaystyle \frac{0+0+0+0.18+0.71+64.82}{100}}=0.6571.$$

Fineness modulus of glass powder:

$$FM={\displaystyle \frac{0+0+0.36+4.29+12.68+79.64}{100}}=0.9697.$$

In this study, the half-cell potential method (Figure 8) was employed as a non-destructive technique to evaluate the likelihood of corrosion activity in the reinforced concrete specimens. This test, based on the guidelines of ASTM C876, involves measuring the electrical potential of the embedded carbon steel bar (diameter 10 mm, Grade 420) relative to a reference electrode (copper/copper sulfate, Cu/CuSO₄) on the surface of the concrete. The readings provide insight into the electrochemical condition of the reinforcement, helping to estimate whether corrosion is actively occurring, possibly occurring, or unlikely. The half-cell potential test was applied to a total of seven distinct types of concrete mixtures:

1

Standard mix;

2

Silica fume mix (20% SF);

3

Fly ash mix (15% FA);

4

Slag mix (10% slag);

5

Glass powder mix (20% GP);

6

Mix of glass powder and fly ash (10%GP + 10%FA);

7

Mix of glass aggregate, glass powder, and fly ash (5%GA + 10%GP + 10%FA).

Each mix type was tested using three separate concrete samples, resulting in a total of 21 specimens evaluated. All samples were cast, cured, and tested under consistent conditions to ensure the comparability of results.

The testing produced a range of potential values across mixtures, allowing the corrosion risk to be classified into three categories:

• Values above −200 mV indicated low probability of corrosion.
• Values between −200 mV and −350 mV represented uncertain or intermediate risk.
• Values below −350 mV were associated with a high probability of active corrosion.

From this procedure, important observations were made regarding the performance of each mix design. While some specimens showed consistent electrochemical stability, others exhibited areas with highly negative readings, indicating potential corrosion activity. These differences helped assess the impact of various supplementary cementitious materials and recycled content on the concrete durability and corrosion resistance.

To create corrosion in the carbon steel bars with a 10 mm diameter, the bar was inserted in a fresh concrete cube (100 × 100 × 100 mm³, Figure 9) specimen during the cast. After 24 h in the air, all specimens were submerged in natural water for 28 days except for the top of specimens for air penetration, as shown in Figure 10. Then, they were dried in a room with ambient temperature of 24° Celsius for 28 days. The natural water had components to facilitate corrosion, in particular, high total dissolved solids (TDS) and high electrical conductivity (EC) that can enhance conductivity [44]. The water ingredients that play the largest role in corrosion are listed in

Table 5. The ingredients of natural water that most enhance corrosion.

Parameters	Value	Unit
pH	7.50	–
Total Dissolved Solids (TDS)	2000	mg/L
Electrical Conductivity (EC)	3.15	dS/m
Chloride (Cl−)	354	mg/L
Sodium (Na)	207	mg/L

.

3. Results

The results of the mechanical properties of all specimens with their volume and procedure compliance with ASTMs are listed in

Table 6. Compressive strength test, flexural test, and splitting tensile test results.

	Shapes and Dimensions of Specimens
	Cylinder: 100 mm Diameter, l = 200 mm		Beam: 100 × 100 × 500 mm3 l = 300 mm		Cylinder: 100 mm Diameter, l = 200 mm
	Compressive Strength Test		Flexural Test		Splitting Tensile Test
Specimens	Peak Load	Compressive Strength	Peak Load	Modulus of Rupture (MOR)	Peak Load	Splitting Tensile Strength
	(KN)	(MPa)	(KN)	(MPa)	(KN)	(MPa)
Standard	186.75	23.78	19.40	5.82	39.57	1.26
20% SF	295.08	37.57	24.29	7.29	68.10	2.17
15% FA	295.75	37.66	23.49	7.05	74.43	2.37
10% Slag	410.75	52.30	32.29	9.66	87.05	2.77
20% GP	250.08	31.84	23.90	7.17	55.97	1.78
10%GP + 10%FA	313.38	39.90	26.16	7.85	69.20	2.20
5%GA + 10%GP + 10%FA	351.63	44.77	33.25	9.98	93.97	2.99
Equations	$Compressive Strength={\displaystyle \frac{P}{A }}$		$MOR={\displaystyle \frac{Pl}{b{d}^2}}$		$Splitting Strength={\displaystyle \frac{2P}{\pi ld }}$

P = peak load; A = cross area; l = length; d =diameter; b = width; d² = depth².

.

3.1. Compressive Strength Test Results (Figure 11)

The outcomes indicate that the addition of supplementary cementitious materials (SCMs) and recycled materials significantly improved the performance of the concrete mixtures compared to the standard mix, which recorded the lowest average compressive strength result, approximately 23.78 MPa, providing a baseline for comparison. Of all the modified mixtures, the one containing 10% slag exhibited the highest compressive strength result, reaching approximately 52.34 MPa. The compressive strength of a mix containing 20% SF yielded a similar result around 37.57 MPa compared to the mix containing 15% FA, 37.66 MPa, indicating their significant role in enhancing compressive strength.

Further, the 20% GP mix improved the strength levels (approximately 31.84 MPa), demonstrating that a high GP content significantly increases the strength when properly distributed. It also indicates that this material contributes positively when used within optimal limits. The concrete with 10% GP and 10% FA added, significantly increased the compressive strength to 39.9 MPa, indicating synergy between the two types of SCM concrete that enhanced the compressive performance.

Interestingly, the mixture containing 5% GA, 10% GP, and 10% FA achieved strengths of approximately 44.77 MPa, outperforming the standard mix and several other mixtures. This suggests that the use of multiple materials can achieve adequate performance, likely due to the matrix densification and pozzolanic activity of SCMs, despite the partial replacement of natural sand with recycled fine glass aggregate.

3.2. Flexural Strength Test Results (Figure 12)

The results provide insight into the flexural strengths (Modulus of Rupture) of concrete mixtures modified with supplementary cementitious materials (SCMs) and recycled components. The 5%GA + 10%GP + 10%FA mix and 10% slag mix recorded the highest modulus of rupture, reaching 9.98 MPa, and 9.69 MPa, respectively, clearly outperforming all other mixtures. This indicates a significant improvement in crack resistance and structural integrity under flexural loads.

The 20% SF, 20% GP, and 15% FA mixtures exhibited similar values of 7.29 MPa, 7.17 MPa and 7.05 MPa, respectively. Their results are better than the standard mix with 5.82 MPa. These results indicate that three types of SCM effectively improve the interfacial transition zone (ITZ) and matrix densification, contributing to better tensile stress distribution and increased flexural strength. In addition, when combined 10%GP with 10%FA, the modulus of rupture improved significantly (7.85 MPa), likely due to complementary pozzolanic effects and improved particle packing.

3.3. Tensile Strength Test Results (Figure 13)

These results provide essential insights into the ability of concrete mixtures to resist cracking and tensile stresses, which are critical factors for the long-term durability of reinforced concrete structures. The standard mix recorded the lowest tensile strength, 1.26 MPa, establishing a basis for performance comparison. All the modified mixtures exhibited higher tensile strength values, demonstrating the positive effects of incorporating supplementary cementitious materials (SCMs) and recycled components. The 10% slag mix achieved a high tensile strength with 2.77 MPa, highlighting the strong contribution of slag to tensile strength.

Importantly, both the 20% GP mix and 15% FA mix achieved a tensile strength of 1.78 MPa and 2.37 MPa, respectively, indicating that GP and FA can be effectively used as partial cement replacements without adversely affecting the tensile properties, especially when combined with other SCMs. Therefore, the blend of 10% GP and 10% FA achieved 2.2 MPa, demonstrating a significant improvement from mixing, compared by using GP only. In addition, the 20% SF mix achieved 2.17 MPa, demonstrating a significant improvement compared to the standard. These results can be attributed to the pozzolanic interactions of SF and FA, which enhance the bond between the cement paste and aggregate while improving the pore structure. The 5%GA + 10%GP + 10%FA mix achieved the highest tensile strength of 2.99 MPa. This result complies with the high compressive and flexural performance for a promising high quality concrete material.

3.4. Corrosion Test Results (

Table 7. Average results of the corrosion test.

	mV (Zone)
Concrete Type	<−350 (Active Corrosion)	−350 to −200 (Uncertain Corrosion)	>−200 (No Corrosion)
	Probability of Corrosion (%)			Average RH (%)
Standard	33.0	58.0	9.0	54.32
20% SF	26.9	67.3	5.8	49.10
15% FA	0.0	87.5	12.5	58.87
10% Slag	8.4	91.6	0.0	57.00
20% GP	8.4	91.6	0.0	53.75
10%GP + 10%FA	79.2	20.8	0.0	49.58
5%GA + 10% GP + 10% FA	33.4	58.3	8.3	50.91

, Figure 14)

The half-cell potential measurements indicate clear differences in corrosion risk among the various concrete mixtures. According to ASTM C876, the corrosion potential can be categorized as follows:

• >–200 mV: 90% probability of no corrosion;
• –200 mV to –350 mV: uncertain corrosion activity;
• <–350 mV: 90% probability of active corrosion.

The 20% SF mix samples showed improved resistance, with only 26.9% in the high-risk range and a majority of 67.3% in the uncertain zone (−350 mV to −200 mV). This indicates moderate improvement but is not the best alternative. The 15% FA mix samples showed excellent performance with 0% of samples in the high-risk category and 87.5% in the uncertain zone, with 12.5% in the probability of no corrosion (>−200 mV), suggesting improved densification and reduced permeability. The 10% slag mix samples and 20% GP mix samples both performed very well, with only 8.4% in the high-risk zone and over 91% in the uncertain-to-safe range (−350 mV to −200 mV). This suggests that both materials effectively reduce the permeability and protect reinforcement.

However, the combination of 10% GP and 10% FA performed the worst, with 79.2% of samples falling in the active corrosion zone (<–350 mV), indicating these were not corrosion-resistant mixes. Interestingly, the addition of fine glass aggregate to glass powder and fly ash (5%GA + 10%GP + 10%FA) increased the performance, showing a corrosion pattern similar to the standard mix, which is about a 33% probability of active corrosion. This suggests that recycled fine glass aggregate may have introduced lower permeability or fewer flaws that increased the corrosion resistance.

Finally, the average relative humidity percentage (RH) for each mix was calculated via the corrosion test (Table 7). However, the RH did not affect the corrosion resistance, because the range was close: between 49 and 59. For instance, the 20% SF specimen showed better corrosion resistance than the 10% GP with 10% FA mix specimen, even though both specimens had approximately the same RH, 49.1% and 49.5%, respectively (Figure 14).

4. Discussion

The superior performance of slag (10% slag mix) highlights its potential in high-strength applications, while glass-based materials, such as powder or fine aggregate, show promise in sustainable construction, as can be seen in Figure 15 in terms of the compressive strength, modulus of rupture, and splitting tensile strength. In addition, the silica fume (20% SF mix) and the fly ash (15% FA mix) enhance the performance of the concrete’s strength. The major reason for the strong mechanical properties for these mixtures is because these admixtures contain silica (SiO₂), alumina (Al₂O₃), or calcium oxide (CaO) as provided in Table 2. Especially, silica fume and glass have the maximum amount of SiO₂ and considered the major component. Another reason that made the slag have the best compressive strength result that has the highest amount of CaO. CaO reacts with water in fresh concrete to form calcium hydride (Ca(OH)₂). Ca(OH)₂ is essential for the hydration process in cement to produce stronger and more durable concrete structures (Equation (2)). Since, around 25% to 50% of the weight of the fresh cement paste weighted by calcium hydroxide (Ca(OH)₂) that reacts with SiO₂ or Al₂O₃ with the presence of water (H₂O) for producing chemical reactions as can be represented by Equations (3) and (4) [45,46,47,48,49,50]:

CaO + H₂O → Ca(OH)₂,

(2)

x Ca(OH)₂ + y SiO₂ + z H₂O → x CaO⋅ y SiO₂⋅ x + z H₂O (C-H-S),

(3)

x Ca(OH)₂ + y Al₂O₃ + z H₂O → x CaO∙ y Al₂O₃∙ x + z H₂O (C-A-H).

(4)

where x, y, and z represent numbers for balancing the chemical equation.

These pozzolanic reactions produce extra calcium silicate hydrate (C-S-H) or calcium alumina hydrate (C-A-H), which fills the concrete pores. This process makes concrete to be less permeable against chemical attacks, which in turn becomes a denser, stronger and more durable material.

Comparing the best results with the results of the literature review (Table 1) in terms of compressive strength, the 10% slag mix had approximately the same result, 52.30 MPa and 48.05 MPa, respectively. Also, the 10% FA mix was close to the results from the literature review, at 37.66 MPa and 38 MPa, respectively. Surprisingly, 10%GP + 10%FA is better than the standard mix in the literature review by 19%. However, the compressive strength of the 20% SF mix was 46% less than the results in the literature review because the literature review standard mix’s result is better than the result of the standard mix in this study by 76% (Figure 15).

The flexural strength results (modulus of rupture) show that slag (10% slag mix) and 5%GA + 10%GP + 10%FA mix also had the highest value. The 10%GP + 10%FA mix significantly enhanced the ability of concrete to resist flexural stresses (modulus of rupture). While glass powder (20% GP mix) alone had good flexural capacity (modulus of rupture) at high replacement levels, its performance can be improved when used in combination with other reinforced concrete materials such as 10% GP with 10% FA. Positively, adding glass aggregate 5% GA to 10%GP and 10% FA appears to be beneficial to the flexural performance. The modulus of rupture values of the 15% FA mix and 20% SF mix improved by 25% and 21%, respectively, comparing with the standard mix (Figure 15).

The splitting tensile strength results confirm that SCMs, such as fine glass aggregate, glass powder, slag, fly ash, and silica fume, significantly improve the tensile strength of concrete, reducing the risk of cracking under tensile stress. When carefully incorporated, recycled materials such as glass powder and fine aggregates (5%GA + 10%GP + 10%FA mix), which had the best result, can positively contribute to the tensile performance, supporting the design of sustainable and resilient concrete. Also, 10% slag had the second-best performance because its high calcium oxide content promotes additional C-S-H gel formation, improving cohesion and crack resistance (Figure 15).

Overall, these results demonstrate the feasibility of SCM concrete and recycled materials to produce environmentally sustainable concrete. The results reveal that the mechanical properties of the standard mix increase gradually by modifying it with, in order of effectiveness, (1) 20% GP, (2) 20% SF, (3) 15% FA, (4) 10%GP + 10%FA, (5) 5%GA + 10%GP + 10%FA, and (6) 10% slag (Figure 15). However, the 15% FA mix produced the best corrosion resistance (Figure 14). In addition, mixtures containing 10% slag or 20% GP showed the second-best performance against corrosion. The third-best performance against corrosion is the 20% SF mix, which all previous mixtures complied with literature review. In contrast, the 5%GA + 10%GP + 10%FA mix did not perform very well against corrosion and was like standard mix. The worst performance against corrosion was with 10%GP + 10%FA mix. Finally, the 10% slag mix and 5%GA + 10%GP + 10%FA mix showed a significant improvement in terms of the compressive strength, flexural, and splitting tensile tests. These insights are critical for improving concrete mixtures designed for structural and sustainable applications.

5. Conclusions

In conclusion, this study addressed a critical issue in modern construction, the durability of reinforced concrete, a material that is extensively used in the construction of buildings, bridges, roads, and other infrastructure. The corrosion of the steel reinforcement within concrete is a major factor that negatively impacts its long-term performance, safety, and overall service life. This process not only compromises the structural integrity of concrete but also leads to significantly increased maintenance and repair costs. The porous nature of concrete allows water, air, and other harmful elements to infiltrate, which in turn accelerates the corrosion of the steel reinforcement, further weakening the structure.

This proposal explored an innovative solution to this problem by investigating the use of recycled glasses as fine aggregate (sand) or as partial replacement of cement (powder), alongside various additives, to enhance the concrete’s resistance to corrosion and to prevent the penetration of water and air. By incorporating recycled materials into the mix, the project aimed to not only improve the durability and longevity of concrete but also reduced the environmental impact of construction activities. Recycled aggregates reduce the demand for virgin raw materials, thereby conserving natural resources and minimizing waste, contributing to more sustainable and environmentally responsible construction practices.

The potential benefits of this research are far-reaching. By improving the resistance of concrete corrosion and environmental damage, the study could help extend the service life of infrastructure, reducing the frequency of costly repairs and replacements. This, in turn, can lead to significant savings for both the public and private sectors, and ensure that infrastructure remains safe and reliable for longer periods. Furthermore, the incorporation of recycled materials supports the shift towards a circular economy in the construction industry, promoting sustainability by reusing materials that would otherwise contribute to landfill waste.

In a broader societal context, the findings from this study could lead to safer, more durable infrastructure, which is crucial for the well-being of communities. The enhanced durability of reinforced concrete structures would improve the resilience of public infrastructure against natural disasters, extreme weather, and the general wear and tear of daily use. Ultimately, the work undertaken in this study could serve as a significant step towards revolutionizing the construction industry by producing more cost-effective, sustainable, and reliable materials, which will have a lasting positive impact on both the economy and the environment for future generations.