Search Results (44)

The management of washing water from concrete plants is a growing environmental and industrial concern due to its high alkalinity and the presence of suspended solids, chemical admixtures, and dissolved salts. This study investigates the impact of collected and recycled concrete plant washing water on the physical, chemical, and mechanical properties of mortars. Two types of wastewater were analyzed: (1) collected water (CW), obtained from settling tanks with residual suspended particles and chemical compounds, and (2) recycled water (RW), subjected to a complete treatment process including pH stabilization and solid particle removal. The effects of these waters were compared against potable water (PW) through a comprehensive experimental program evaluating the porosity, density, shrinkage, and mechanical performance of mortars. The results indicate that using CW and RW leads to increased porosity, higher shrinkage, and a reduction in compressive and flexural strength, with RW having a more pronounced impact. These changes are attributed to the chemical composition of the water, which affects cement hydration and matrix densification. Despite these drawbacks, the proper treatment and controlled usage of such waters may offer sustainable alternatives to potable water in concrete production, contributing to resource conservation and environmental sustainability. Full article

This research aims to identify an eco-friendly and low-mass substitute for fine aggregate (FA) in self-compacting concrete (SCC). The study specifically examines the potential of waste foundry sand (WFS) as an FA replacement. The primary objective is to explore the impact of processed WFS in SCC, addressing both the WFS disposal issues and enhancing the environmental performance of SCC. After collecting the WFS, it was sieved, segregated, washed thoroughly with water, and then oven dried to remove all clay, carbon, and hazardous content. Treated foundry sand (TFS) is utilized as a substitute for FA in SCC. This study examines the effects of TFS on SCC’s strength, flowability, durability, and microstructural characteristics. Various proportions of TFS are investigated, including replacing 0, 10, 20, 30, 40, and 50% of FA by weight with TFS in the concrete mixture. This research demonstrates that TFS can effectively replace FA in improving the flowability and passing ability of SCC. Furthermore, the findings on SCC’s strength and durability after incorporating TFS suggest that using 30–40% TFS is optimal, as it does not negatively impact the structural performance of SCC. Alternatively, the use of TFS in SCC results in a dense microstructure, improved gel formation, and better bonding of the constituents of ingredients used in SCC. Overall, the results of this study reveal that the use of TFS in SCC can help reduce the amount of waste and improve its sustainability. This also shows that the process can reduce the density of the mix. Full article

In order to solve the problems of the large-scale resource utilization of iron ore waste rock, waste rock is used to prepare green building materials, but it needs to be further promoted for use in high-strength concrete. In this study, high-strength concrete was prepared using iron ore waste rock as coarse and fine aggregates combined with solid waste-based cementitious materials. The mechanical and durability properties of washed and unwashed concrete with two types of aggregates were compared, including compressive strength, freeze resistance, chloride ion resistance, carbonation resistance, pore distribution, microstructural characteristics, and environmental and economic benefits. The results indicated that water-washing pretreatment significantly reduced the stone powder content of waste stone aggregate from 14.6% to 4.5%, which had a significant effect on the basic properties of concrete. The compressive strength of concrete with water-washed waste rock aggregate was 61 MPa, 64.9 MPa, and 68.8 MPa at 28, 56, and 360 days, respectively, with long-term stability. The washed aggregate concrete had a porosity of less than 4%, freeze-resistant grade of F200, 28 d electrical flux <500 C, and a carbonation depth of less than 10 mm. The improved performance of the washed aggregate concrete was attributed to the fact that after washing pretreatment, the water absorption of the aggregate was reduced, the cementitious materials were fully hydrated, and the internal microstructure was denser. The high-strength concrete prepared in this study effectively used iron ore waste rock and solid waste-based cementitious materials, which not only reduces environmental burden but also provides basic data references for future engineering applications using iron ore waste rock aggregate concrete. Full article

To address SDG12 (ensure sustainable consumption and production patterns), and to provide technical evidence for alternative concrete constituents to traditional natural river sand, stone fine aggregate (SFA), brick fine aggregate (BFA), ladle-refined furnace slag aggregate (LFS), recycled brick fine aggregate (RBFA), and washed waste fine aggregate (WWF), ready-mix concrete plants were investigated. Concrete and mortar specimens were made with different variables, such as replacement volume of natural sand with different alternative fine aggregates, water-to-cement ratio (W/C), and sand-to-aggregate volume ratio (s/a). The concrete and mortar specimens were tested for workability, compressive strength, tensile strength, and Young’s modulus (for concrete) at 7, 28, and 90 days. The experimental results show that the compressive strength of concrete increases when natural sand is replaced with BFA, SFA, and LFS. The optimum replacement amounts are 30%, 30%, and 20% for BFA, SFA, and LFS, respectively. For RBFA, the compressive strength of concrete is increased even at 100% replacement of natural sand by RBFA. For WWF, the compressive strength of concrete increases up to a replacement of 20%. Utilizing these alternative fine aggregates can be utilized to ensure a circular economy in construction industries and reduce the consumption of around 30% of natural river sand. Full article

This study explores the utilization of municipal solid waste incineration fly ash (MSWIFA) in geopolymer concrete, focusing on compressive strength and heavy metal leachability. MSWIFA was sourced from a Shenzhen waste incineration plant and pretreated by washing to remove soluble salts. Geopolymer concrete was prepared incorporate with washed or unwashed MSWIFA and tested under different pH conditions (2.88, 4.20, and 10.0). Optimal compressive strength was achieved with a Si/Al ratio of 1.5, water/Na ratio of 10, and sand-binder ratio of 0.6. The washing pretreatment significantly enhanced compressive strength, particularly under alkaline conditions, with GP-WFA (washed MSWIFA) exhibiting a 49.6% increase in compressive strength, compared to a 21.3% increase in GP-FA (unwashed MSWIFA). Additionally, GP-WFA’s compressive strength reached 41.7 MPa, comparable to that of the control (GP-control) at 43.7 MPa. Leaching tests showed that acidic conditions (pH 2.88) promoted heavy metal leaching, which increased over the leaching time, while an alkaline environment significantly reduced the leachability of heavy metals. These findings highlight the potential of using washed MSWIFA in geopolymer concrete, promoting sustainable construction practices, particularly in alkaline conditions. Full article

This study examines the potential use of wash fines, a waste product from concrete plant cleaning, as supplementary cementing materials (SCMs) in mortars. The main objective is to assess the feasibility and benefits of this incorporation in terms of technical performance and environmental impact. Extensive tests were carried out on different mortar formulations, incorporating varying rates of washing fines (0%, 10%, 20%, 30%) as a partial replacement for cement. This choice of replacement is prompted by the fineness of washing fine particles. The properties studied included compressive and flexural strength, porosity, density, water absorption, shrinkage and fire resistance. The results show that the incorporation of washing fines increases porosity and decreases mortar density. There was also a decrease in mechanical strength and fire resistance as the substitution rate increased. However, the use of washing fines enables a significant reduction in the mortar’s carbon footprint, reaching up to 29% for the formulation with 30% substitution. This study demonstrates the potential of washing fines as an alternative SCM, as part of a circular economy approach to reducing the environmental impact of the concrete industry. However, it underlines the need to optimize formulations to maintain acceptable technical performance. Full article

Clays are components in the fine portion of aggregates, less than 75 microns in size (micro-fines), which are usually washed away when producing coarse or fine (manufactured sand) aggregates in quarries. When marginal sources of aggregates are being used, the content of this washed portion can be quite high, and there is an incentive to keep as much of it in the aggregate, including the clays. The present paper presents a comprehensive treatment of the role of clays in terms of the characterization of their composition and quantification of their effects on the rheological and mechanical properties of cementitious systems, as well as the means to mitigate deleterious influences. It is shown that the strategy for neutralizing the effect of micro-fines containing clays on increased water demand in concrete can be quantified in terms of the combination of their content in concrete and their nature as characterized by the methylene blue value (MBV); this is a more rational approach to considering their influence than their content in specific aggregates as specified in standards. The effect of low and medium MBV aggregates on the water requirement can be neutralized by lignosulfonates when their content in the concrete is below a threshold value of about 150 kg/m³; polycarboxylates (PC) are required at higher contents; for high MBV aggregates, a combination of PC and clay mitigating admixture (CMA) is required. It is also demonstrated that with proper treatment, such micro-fines can be turned into useful fillers, enhancing the strength of concrete and thus also serving as a means for reducing cement content. Full article

The reasonable and effective application of waste tires and discarded concrete in concrete is an important branch of green concrete development. This paper investigates the effects of the inorganic modification mode on the basic mechanical properties of rubber recycled concrete based on indoor tests. Inorganic modification, such as water washing, acid washing, and alkaline washing modification, was mainly used to treat and modify rubber particles. The factors affecting the compressive strength, the splitting tensile strength, the flexural strength, the axial compressive strength, and the modulus of elasticity of modified rubber recycled concrete were analyzed. The study results show that the incorporation of recycled aggregates and rubber reduced the mechanical properties of concrete, with the compressive and splitting tensile strengths showing the greatest reductions of 27.36% and 27.24%, respectively. Three modification methods significantly improved the mechanical properties of rubber recycled concrete. The alkali washing modification method was the most effective, maximally improving the mechanical properties of rubber recycled concrete by 7.53–15.51%. The effects of the three modifications on the mechanical properties of concrete were ranked as follows: alkali washing > acid washing > water washing. This study provides a data basis for the practical application of rubber recycled concrete in engineering and a test basis for the development of green concrete. Full article

Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze–thaw conditions. Recycling 5–16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze–thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze–thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates. Full article

This study examines the properties of ordinary and high-strength fiber-reinforced pervious concrete, aiming for a 28-day compressive strength exceeding 40 MPa with a target porosity close to 15%. Utilizing glass fiber (at 0.25% and 0.5% volume ratios) and steel fiber (at 1% and 2%), the study conducts mechanical and abrasion resistance testing on pervious concrete specimens. Sand dust clogging experimental simulations assess permeability coefficients for both application and maintenance purposes, revealing optimized maintenance, including vacuum cleaning and high-pressure washing, can restore water permeability to over 60%. The specific mix designs demonstrate high-strength pervious concrete achieves a 28-day compressive strength ranging from 40 to 52 MPa, with corresponding porosities ranging from 7% to 16%. Results highlight the significant impact of the ASTM C1747 impact abrasion test, where ordinary pervious concrete exhibits a cumulative impact abrasion rate reaching 60%, contrasting with approximately 20% for other high-strength specimens. Full article

The plasma polymerization of hexamethyldisiloxane (HMDSO) leads to the environmentally friendly fabrication of water-repellent coatings through a vapor-phase surface functionalization process using alternatives to the controversial perfluoroacrylate precursors. However, the durability of these coatings is their Achilles’ heel, which requires an in-depth study of the relationship between the structure and properties of these thin films in order to propose concrete solutions for the fabrication of fluorine-free water-repellent textiles. In this context, HMDSO plasma polymers have been deposited on cotton fabrics in an original reactor that allows easy tuning of temporal and spatial parameters of the glow discharge. The functionalized fabrics were characterized to gain insights into the chemical composition of the coatings, their morphology and, above all, their adhesion properties. Interestingly, the results after washing tests revealed a significant dependence of the durability of the superhydrophobic property on the elastic modulus of the deposited polymer. The formation of some radicals at the substrate–thin film interface in the early stages of deposition also correlates with some results. These relationships between the operating conditions of the plasma polymerization, the interfacial properties and the performances of the functionalized fabrics, but also the characterization methodology developed in this work, can undoubtedly serve the engineering of water-repellent fluorine-free coatings on fabrics with optimal durability. Full article

Tomato brown rugose fruit virus (ToBRFV) is a contact-transmitted tobamovirus affecting many tomato growing regions of the world. This study investigated the effects of different glasshouse surfaces on the survival of the virus; the efficacy of different disinfectants; and heat treatment against ToBRFV (surfaces included steel, aluminium, hard plastic, polythene, glass and concrete). A bioassay followed by ELISA was used to check virus viability. ToBRFV survived for at least 7 days on all surfaces tested and on some for at least 6 months. The virus survived for over two hours on hands and gloves. Hand washing was shown to be unreliable for the removal of the virus. Glutaraldehyde and quaternary ammonium compound disinfectants were effective at one hour on all surfaces. Some other disinfectants were effective at one hour of contact time, on all surfaces except concrete. Sodium hypochlorite was partially effective against ToBRFV, even on concrete. A 5 min soak of plastic trays in water at 90 °C was effective at denaturing ToBRFV; however, 5 min at 70 °C was not. Heating infected sap showed the thermal inactivation point to be 90 °C, confirming the hot water treatment results and showing that deactivation was due to the heat treatment and not a washing effect of the water. Full article

In the concrete manufacturing industry, a large amount of waste is generated. Such waste can be utilised in the production of more sustainable products with a low carbon footprint. In this study, concrete sludge, a difficult-to-utilise waste that is obtained from residual concrete by washing a concrete truck, was investigated. During washing, aggregates from the concrete mixture are separated, and the remaining insoluble fine particles combine with water to form concrete sludge. Dried and wet concrete sludge were used in the tests. Samples with different compositions were produced with dried and wet concrete sludge, cement, superplasticiser, and tap water. Seven cement pastes with different compositions were made by partially replacing cement with dried concrete sludge (0%, 5%, 10%, 15%, 20%, 25%, and 30%). In compositions with wet concrete sludge, cement was replaced by the same amounts as in the case of dried concrete sludge. The slump, setting time, and their changes with different amounts of concrete sludge were determined for fresh cement pastes. It was found that with different forms of concrete sludge, the technological properties of the mixtures change, and the setting time decreases. The density and compressive and flexural strength results were confirmed by SEM and XRD tests. The research results show that dry concrete sludge causes the deterioration of the mechanical properties of cement stone, while wet concrete sludge improves the mechanical properties of cement stone. However, it was found that replacing 5% cement with dry concrete sludge does not significantly affect the properties of hardened cement stone. In mixes with wet concrete sludge, the recommended amount of replaced cement is 10%, because the technological properties of the mixture are strongly influenced by larger amounts. Full article

At present, in order to comply with the development of the “the Belt and Road Initiatives”, the country is accelerating the pace of construction and increasing the demand for construction river sand. However, the quality of construction river sand is uncontrollable, and its shape is very similar to that of weathered sand. Therefore, using inferior weathered sand and mixed sand as inferior substitute sand in the market is prohibited, resulting in an increase in the difficulty coefficient of quality control of concrete fine aggregate in actual projects. This lays hidden dangers for the construction quality of the project. It is urgent to improve the quality control, testing, and detection process of river sand. Due to the long-term weathering of weathered sand, its density is small, and there are many pores, which leads to the material’s water absorption rate is higher than that of standard sand and river sand during fluidity tests. This paper takes this as a breakthrough point, reveals the variation law of fluidity loss under different variables, and explores a method for effectively screening low-quality sand and gravel. Through the silt content test (screening and washing method), the low-quality sand is preliminarily screened out, the mortar ratio is designed, and the fluidity test is carried out to compare the difference in fluidity loss of different types of mortar; determine the loss threshold range (mobility loss ≤ 15 mm) according to the mobility test results of the control group, and determine the qualification standard by comparing the measured mobility loss of the unknown sample with the loss threshold range. When the mobility loss is within the loss threshold range, the sample is qualified river sand. Otherwise, it is weathered sand or chowder sand. This method establishes a complete detection scheme for distinguishing weathered sand and river sand through mud content tests and mobility loss tests, solves the difficult problem of river sand quality control in engineering applications, and effectively eliminates the phenomenon of using low-quality weathered sand as river sand in the sand and gravel material market, thus avoiding congenital defects in concrete homogeneity. Full article

This paper presents new software (Concrelife) capable of reliably simulating chloride ions penetration in reinforced concrete from different environments in the most common 1-D rectangular geometry scenarios. Its numerical solution is obtained from the simulation of models whose structure is based on Network Simulation Method. These models are generated by the program itself and run in the powerful free code NgSpice. The mathematical model of the problem includes the formation of bound chloride, precipitated chloride, reduction of porosity, saturated and unsaturated conditions, etc. All this allows tackling all kinds of scenarios, such as successive changes in concentration and temperature at the boundary, wet-drying cycles, washing of structures, etc. Concrelife has been developed with a pleasant window environment, intuitive and easy for a user not expert in numerical techniques, both for the introduction of data and for the graphic representation of the results, which include the spatial and temporal concentration of all species of chloride, porosity, water content in pores etc. To test and verify the results of the software, applications are presented to real scenarios. Full article