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This study focuses on the synthesis of a monocarboaluminate (MCA)-based binder by treating marble waste (MW) powder with sodium aluminate (SA). The aim is to investigate the influence of various parameters, including the alumina modulus (MA) of SA, different contents of calcined clays with varying alumina levels, and curing temperatures, on the performance and phase composition of the resulting binder. The results demonstrate that the combination of SA and MW leads to the formation of an MCA-based binder, which exhibits a high compressive strength of up to 28 MPa after seven days of curing. Additional phases such as gibbsite, pirssonite, and gaylussite are observed, indicating the occurrence of a cationic exchange reaction between MW and SA, as confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The stability of the resulting binder is primarily influenced by the MA value, with higher values associated with greater stability. Regardless of the type of calcined clay used, incorporating calcined clay results in the formation of a calcium aluminate silicate hydrate (CSAH) phase alongside MCA, contributing to the improved stability of the hardened binder over time. Notably, calcined clay with a higher alumina content exhibits the highest strength at all curing ages. Furthermore, increasing the curing temperature up to 100 °C significantly enhances the early strength, which correlates with the formation of the kotoite phase at the expense of the MCA phase. [ABSTRACT FROM AUTHOR]

Recycled expanded polystyrene (EPS) beads were used as a partial replacement for concrete mix components to develop lightweight concrete mixes with good thermal insulation properties. The replacement ratios were 50, 55, and 60% of the total mix volume. Workability, compressive, flexural, splitting tensile strengths, and thermal conductivities were evaluated. Two casting methods were investigated (with and without compaction). The results showed that using the recycled EPS beads significantly reduced the density, thermal conductivities, and mechanical properties of the mixes. Compared to the control mix, the decrease in the density ranged between 37% and 46% for the compacted samples and between 52% and 60% for the un-compacted samples. The thermal conductivities decreased by about 63% to 74% for the compacted samples and by about 78% to 85% for the un-compacted samples, which makes them efficient in thermal insulation applications. The decrease in the compressive strength ranged from 87% to 94% for the compacted samples and from 97% to 98% for the un-compacted samples. The test results revealed that the compacted samples with 50% and 55% of EPS achieved compressive strengths of 7.2 and 5.1 MPa, respectively. This makes them suitable for environmentally friendly non-structural applications with good thermal insulation properties. [ABSTRACT FROM AUTHOR]

Internal curing (IC) process introduced via a water‐entraining agent using lightweight and porous aggregate has become an essential component in designing high and ultra‐high‐performance concrete (HPC/UHPC). This paper presents experimental results demonstrating the effectiveness of using recycled ceramic tile aggregates (RCTA) derived from waste ceramic tiles as an IC agent for high‐performance structural elements. Previous studies by the author have confirmed the efficiency of both the pre‐saturated recycled porous ceramic coarse aggregate (RPCA) as an IC and shrinkage compensating agents in mitigating autogenous shrinkage and the induced internal self‐stress in HPC mixtures. The main objective of this study is to investigate the effect of two different curing systems (internal curing using the waste ceramic aggregate combined with shrinkage compensating agents) on silica fume (SF) HPC behavior. The shrinkage compensating agents include a combination of shrinkage‐reducing agent (R) and expansive additive (E). The influence of this combined ternary curing system on the mechanical properties, including compressive, flexural, and splitting tensile strengths, modulus of elasticity, autogenous shrinkage, and internal self‐induced tensile stress, were investigated. The obtained results indicate a substantial reduction in the autogenous shrinkage strains magnitude and, consequently, the internal self‐induced tensile stress in the HPC mixtures designed with these two curing systems. It was also found that this combination of the two curing systems resulting in a hybrid curing system, performs much better than the single incorporation of shrinkage‐compensating agents. Besides, a long‐term strengths improvement was recorded for mixtures designed with the RPCA. Incorporating recycled aggregate in the design and production of HPC could further promote concrete sustainability by reducing the amount of virgin extracted non‐renewable minerals, reducing the energy required to extract and process natural aggregates and the CO2 generated, and also reducing solid waste materials disposal. [ABSTRACT FROM AUTHOR]

Bacteria-prompted calcite precipitation enhances concrete strength properties and durability performance by creating nuclei crystals in the concrete pore structure. In this paper, the effect of bacterially treated sugarcane bagasse ash (SCBA)-based concrete on concrete's mechanical and permeability properties has been comprehensively investigated. The SCBA was used in concrete as a partial replacement of normal portland cement at two different replacement levels of 10 and 20%, while bacteria content was kept constant at 105 cells/mL (2.96 x 106 cells/oz.). This study used two different types of bacteria, Sporosarcina pasteurii and Bacillus megaterium from the Bacillus subtilis family. After 28 days of curing in water, the blended cement concrete with 10% SCBA showed higher compressive strength compared to the control mixture. Incorporating B. megaterium and S. pasteurii further improved the compressive strength of concrete by 7 and 10% in SCBA 10% concrete. This compressive strength enhancement is due to the continuous hydration process of cement and the pozzolanic reaction of SCBA in concrete. The addition of bacteria further improves the strength by forming calcite crystals and filling the pore spaces in the concrete. Calcite deposition in the pores of concrete subsequently refines and enhances the microstructure of concrete. The deposition of calcite precipitation in the pores blocks the water permeability, which ultimately reduces the porosity and water absorption of bacteriaincorporated concrete. The incorporation of bacteria in concrete also reduces the penetration of chloride ions compared with the control mixture and the concrete treated with only SCBA. Based on the nuclear magnetic resonance (NMR) spectroscopy analysis, the average chain length of calcium-silicate-hydrate (C-S-H) gel was increased by incorporating SCBA in concrete up to a replacement level of 10%. Further addition of bacteria increases the chain length of C-S-H gel and the degree of cement hydration in concrete. [ABSTRACT FROM AUTHOR]

The use of recycled aggregate in concrete industry has a great potential to reduce demand for natural aggregate and the amount of solid waste dumped at landfill sites. The main objective of this study is to design a concrete made with different proportions of coarse recycled concrete aggregate (RCA) having a similar 28-day design strength to corresponding natural aggregate concrete. Recycled coarse aggregates, obtained by crushing concrete debris from various sources, were used in three proportions of 30, 50, and 100% (by weight) to produce concrete with various water-cement ratios (w/c) and different compressive strength grades. The key mechanical properties and durability performance of concrete produced with portland silica fume (PSF) and RCA were investigated. The RCA used showed inferior mechanical properties (crushing and impact values) than the natural aggregates (NA) and, hence, RCA concrete exhibited slightly lower performance than NA concrete. The results showed that up to 30% coarse RCA had no major effect on the compressive strength of concrete and, thereafter, a gradual reduction in strength with an increase in RCA content was observed. Reducing the w/c of concrete treated with the RCA has led to an enhanced compressive strength, higher resistance to carbonation, and chloride ion ingress. It was also found that, when properly designed, portland cement silica fume (PC-SF) concrete made with different proportions of coarse RCA as substitute of NA may contribute to enhance the durability performance of concrete. [ABSTRACT FROM AUTHOR]

Early-age cracking induced by autogenous shrinkage is still the major problem relating to the use of high-performance concrete (HPC) in reinforced concrete structures. Recent studies have proven that the presaturated recycled porous ceramic coarse aggregate (PCCA) could be successfully used to mitigate autogenous shrinkage of HPC. This study examines the behavior of low-autogenous shrinkage silica fume HPC developed using three different curing techniques. A binary system, made with a combination of shrinkage-reducing agent (SRA) and expansive additive (EX); a hybrid system, containing internal curing provided by the PCCA and SRA combined with EX; and a mono-incorporation of the PCCA were selected for this investigation. The effect of each curing technique on the compressive and splitting tensile strengths, elastic modulus, autogenous shrinkage, and internal self-stress were investigated. The results obtained indicated that HPC produced using 20 to 30% of the PCCA by volume as a partial replacement of the total coarse aggregate content could significantly reduce the magnitude of autogenous shrinkage and the induced self-stress of HPC, whereas 30% of the PCCA seemed to be the optimum content and performed much better than the treated concrete with anti-shrinkage agents. In addition to its efficient shrinkage reducing effect, the incorporation of the PCCA showed a better compressive strength development than the references' mixtures. Moreover, the hybrid curing technique containing (SRA + EX) and 20% of the PCCA provided a better enhancement for shrinkage compensating concrete than either the mono-incorporation or the binary curing system. [ABSTRACT FROM AUTHOR]

The article provides information on a research about the fundamental aspects that result from using mineral admixtures in high-performance concrete (HPC). It focuses on the impact of various pozzolanic admixtures on the process of pore network refinement. It states that HPC is known for the refinement of its capillaries' pores, which induces two opposite phenomena such as improved mechanical performances and self-dessication shrinkage due to high capillary depression. It discusses cement hydration reaction from solid products and a pore system. The study used mercury intrusion porosimetry (MIP) to determine the porosity and pore size distribution of concrete. Results show that refinement of the capillary network and evolution with time are linked with mineral addition type and fineness.

Recycled materials are now widely used in various industrial sectors to enhance sustainability and reduce environmental charges. Using recycled aggregates in concrete production significantly lowers demand for natural aggregates and the amount of solid waste sent to landfills. This paper summarizes the main results of a study undertaken to design low and normal strength concrete with various replacement ratios of coarse recycled concrete aggregates (RCA). To persuade the concrete industry to use recycled materials as one of the main components of concrete produced, the overall mechanical and durability performances of the RCA-concrete should be close or even similar to the concrete made with natural ingredients. The present research adopted an approach that consists of designing a series of low and normal strength with RCA having an equal target 28-day design strength to the corresponding natural aggregates concrete but while varying the water–cement ratios (w/c). Coarse recycled concrete aggregates, obtained by crushing waste concrete debris collected from different construction and demolition waste sources, were used in three different proportions of 30%, 50% and 100% (by weight) to produce new concrete with various w/c ratios and different compressive strength grades. Concrete mixes produced with general use Portland cement and various RCA contents were investigated in terms of their key mechanical and durability performances. The mechanical properties (crushing value) of the used RCA were visibly lower than the natural coarse aggregates (NCA). Thus, RCA-concrete showed lower performance than the NCA-concrete. It was found that by using up to 30% coarse RCA, the mechanical properties of concrete were not significantly affected. Beyond 30% of partial replacement of NCA by the coarse RCA, a continuing decrease in the mechanical performance with an increase in RCA amount was found. However, reducing the w/c ratio of concrete designed with the coarse RCA resulted in a compressive strength improvement, a better resistance to sulphate attack, carbonation, and chloride ion penetrations. Additionally, a proper design of Portland cement concrete produced with various proportions of RCA could also contribute to promoting sustainability in the construction industry and lowering its environmental impact. [ABSTRACT FROM AUTHOR]