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Brick (BR) and roof tile (RT) fine aggregate fractions derived from construction and demolition wastes have a low recycling rate in new construction and building materials. This article assesses their suitability for replacing the limestone aggregate in foam concrete, which helps valorise such fractions and conserve natural limestone resources. Two concrete categories containing or not silica fume (SF) were investigated, while the BR and RT aggregate replacement rates were 10%, 20% and 40%. Tested properties include flow, density, water absorption, porosity, thermal conductivity, mechanical strengths, microscopy, drying shrinkage, resistance to freeze/thaw cycles and elevated temperature. Results showed that the concrete mechanical properties improved when the limestone aggregate was replaced by 10% BR or RT but gradually curtailed at higher addition rates. Such results concorded with the density, water absorption and porosity measurements. Foamed concrete containing BR is more resistant (compared to RT) to drying shrinkage, freeze/thaw cycle, and heat exposure, which was ascribed to the relatively lower BR porosity that improves the concrete mechanical properties and durability. [ABSTRACT FROM AUTHOR]

Limited investigations have evaluated the potential of using layered sections of normal-weight and lightweight concrete (NWC and LWC) mixtures in structural beams and slabs. The main objective of this paper is to assess the flexural strength properties of layered reinforced concrete (RC) beams, which help conserve natural resources and reduce construction weight. Six RC beams cast with different NWC/LWC combinations are tested to determine the damage patterns, concrete strains, ultimate load, displacements at failure, and ductility. The test results showed that the LWC cast in the tension zone (and up to the neutral axis) has a negligible effect on the beam's stiffness and ultimate load since the overall behavior remains governed by the yielding of tensile steel reinforcement. Nevertheless, the deflection at failure and ductility seem to gradually curtail when the NWC is partially replaced by LWC at different elevations across the beam's cross-section. A finite element analysis using ABAQUS software 6.14 is performed, and the results are compared with experimental data for model validation. Such data can be of interest to structural engineers and consultants aiming for optimized design of slabs and beams using layered concrete casting, which helps reduce the overall construction weight while maintaining the structural integrity of members. [ABSTRACT FROM AUTHOR]

This paper assesses the feasibility of concrete mixtures containing high replacement rates of fine and/or coarse waste brick aggregates. Three mixture series prepared with different water-to-cement ratios are tested for workability, compressive strength, split tensile strength, modulus of elasticity, water permea-bility (by capillary or under pressure), and drying shrinkage. Test results showed that the concrete proper-ties remarkably degrade when the coarse natural aggregate fraction (i.e., retained on sieve No. 4) is fully replaced by recycled waste bricks, given their increased porosity that reduces the concrete density and weakens its skeleton. In contrast, the strength and durability remained almost unaltered when the fine natural aggregate fraction was replaced by 50 % recycled waste bricks, and considerably better than equivalent mixtures made using the same amount of recycled fine aggregates derived from hardened waste concrete.

Due to the large increase in human population, the need for more buildings and other amenities is widening. Concrete is considered one of the most abundant and popular materials used in the structure and construction fields. It is known as a composite mix composed of cement and aggregates including fine and coarse and water. Despite its good properties, its capability to be formed in different shapes and its ability to resist severe conditions, concrete will struggle with the presence of extremely high temperatures. So, different types of concrete must be found to resist those challenging conditions. Refractory concrete can be considered a good choice to be used in places exposed to elevated temperatures and severe conditions. Mainly, refractory concrete is made up of ordinary Portland cement replacement well known as refractory cement, specific types of fine and coarse aggregates and are known as refractory or temperature-bearing aggregates and water. To the best authors' knowledge, review papers about refractory concrete are rare. For this reason, more than 65 papers were consulted including many recently published. This review describes the different types of materials used in refractory concrete. Furthermore, the different fresh, hardened, structural, durability and thermal properties of refractory concrete are also included such as slump, density, compressive strength, flexural strength, tensile strength, modulus of elasticity, ultrasonic pulse velocity, shrinkage, mass loss, porosity, water absorption, damage level and thermal conductivity. [ABSTRACT FROM AUTHOR]

This paper assesses the suitability of geopolymers (GPs) for use as adhesives for ceramic tile fixing, including their compliance to the relevant EN 12004 specification. Two series prepared with different percentages of metakaolin (MK), blast-furnace slag (BFS), and limestone materials activated by an alkaline NaOH/Na2SiO3 solution are investigated. Tested properties included the thixotropy, setting, compressive strength, open time, and adhesion bond strength under different exposure conditions (that is, dry, wet, heat, or freezing-and-thawing cycles). Compared to cement-based mortars containing adjusted proportions of cellulose and redispersible polymers, the GPs exhibited higher thixotropy, reflecting additional energy for spreading the material over the substrate, yet better maintenance of the alternating patterns of ripples and grooves at rest. The bond strengths tested under different exposure conditions were remarkably high for the MK-based GP, given the fine MK particle sizes that foster geopolymerization and crosslinking of solid bonds in the hardened structure. The BFS-based GP exhibited relatively lower bond strengths (compared to MK) due to coarser particles. Such results can be of interest to civil engineers and manufacturers of ready-to-use building materials that aim at reducing the portland cement footprint while assuring performance and sustainability of tiling applications. [ABSTRACT FROM AUTHOR]

This study assesses the feasibility of limestone (LS) replacement by recycled fine aggregates (RFAs) on grindability and Portland cement properties. Two RFA types generated from the fine fraction of crushed concrete and ceramic wastes are ground in 22-liters grinding mill at 310 and 400 ± 20 m2/kg Blaine fineness, and then incorporated at 20% and 35% rates in clinker cement mixtures. Because of their porous nature, RFAs required about 22% to 30% less communition energy than LS, which could be advantageous to reduce grinding costs for given Blaine fineness. Mortars prepared with RFA-based cements yielded better strength recovery over time and lower water sorptivity than LS-based cement, either due to promoted hydraulic activity or pozzolanic reactions. The comminution of RFA fillers to 400 ± 20 m2/kg fineness is a viable alternative to mitigate the dilution effect while maintaining similar grinding energy and mechanical strengths as the control 95% clinker cement. [ABSTRACT FROM AUTHOR]

Limited investigations have evaluated the effect of expanded polystyrene (EPS) beads on the structural lightweight concrete properties. EPS offers many features compared to natural or artificial lightweight aggregates including the elimination of aggregate saturation prior to concrete batching, ability to be fabricated on site, consistency in size and quality, and reduced cost. The main objective of this paper is to assess the suitability of finite element (FE) modeling based on deterministic and stochastic approaches to predict the shear strength behavior of reinforced concrete (RC) beams containing EPS additions. Test results showed that the experimental load-deflection properties recorded at failure can be well reproduced using both FE approaches. Nevertheless, the damaged-zone distribution and crack patterns that occur during the loading stages of RC beams cannot be approximated using the deterministic FE approach. In contrast, the stochastic method was quite suitable as it accounted for the concrete heterogeneity and altered spatial mechanical properties (such as compressive strength, splitting tensile strength, and Young's modulus) due to EPS additions. Such data can be of interest to civil engineers seeking to predict the failure patterns and performance of structural lightweight members while reducing the time and resources needed to account for the concrete's strength variability during experimental testing. [ABSTRACT FROM AUTHOR]

This paper assesses the benefits of styrene-butadiene rubber (SBR), steel fibres (SF), and polypropylene fibres (PPF) to mitigate the brittle failure and drop in bond properties due to smooth surface geometries of carbon fibre-reinforced polymer (CFRP) bars embedded in ultra-high performance concrete (UHPC). A ready-to-use UHPC was employed to determine the bond stress vs. slip properties of CFRP and deformed steel bars. Test results showed that the incorporation of SBR is beneficial to alleviate up to 20% the detrimental effect of smooth CFRP geometry, which was attributed to enhanced adhesion along the spiral wounds. The ultimate bond improved by 45% and 87% when 1% of either PPF or SF was added, respectively, given the fibre bridging effect that limits the formation of radial cracks. Also, the ductility improved with fibre additions, reflecting their beneficial role for better transmitting the stresses along the cementitious matrix. The experimental bond strengths determined from the UHPC-Steel specimens are 3- and 3.5-times higher than those computed from EC2 and ACI 318-19 code provisions, respectively. Yet, such ratios dropped to 1.3- and 1.5-times for the CFRP bars, given their lower shear and lug indices that reduced the interaction with surrounding UHPC. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol (PVA) fibers are polymeric filaments used to improve ductility and strain-hardening of cementitious composite mortars and grouts. Limited studies investigated their effect on the structural properties of normal-strength grade concrete mixtures containing coarse aggregates, including the resulting cost-to-performance ratio. For a given fiber volume, results showed that PVA fibers achieved a good compromise between cost and performance, despite their unit price is considered twice and trice higher than polypropylene or steel fibers, respectively. The use of steel fibers induced significant cost increase, however, the overall concrete performance remained lower than the one achieved using PVA fibers. [ABSTRACT FROM AUTHOR]

Limited studies investigated the structural properties of concrete containing cross-linked polyethylene (XPE) plastic wastes derived from thermosetting polymers. The XPE wastes cannot be recycled given their infusible and insoluble natures in the melt state, reflecting the need for sustainable disposal alternatives in the construction industry. The main objective of this paper is to assess the effect of XPE on the bond to embedded reinforcement and shear strength of reinforced concrete beams without stirrups. Test results showed that the ascending part of the bond stress vs. displacement curves is softened with XPE additions, which led to reduced ultimate bond strength to embedded rebars. Such additions also reduced the ultimate shear load and post-diagonal cracking resistance of reinforced concrete beams. The incorporation of 0.5% to 1% steel fibers, by volume, was efficient to delay the formation of cracks, which improved the concrete bearing capacity and aggregate interlock component of shear strength. [ABSTRACT FROM AUTHOR]