High-strength concrete (HSC) makes up the vast majority of materials used in the construction sector due to its exceptional mechanical characteristics and outstanding long-term behaviour. However, in cement-based materials with a low water-to-binder ratio (w/b), excessive autogenous shrinkage has become a prevalent issue. This work suggests the sustainable use of recycled concrete aggregate (RCA) to internally cure HSC in order to reduce autogenous shrinkage during the hydration and curing processes. RCA was employed with various volumetric replacement percentages with natural coarse aggregate as a water storage agent (0%, 8%, 16%, 24%, 32%, 50%, 75%, and 100%) under sealed and unsealed conditions. The efficiency of the adopted materials for internal curing was investigated by determining the autogenous shrinkage in addition to unconfined compressive and flexural strength. The laboratory results reveal that the studied properties significantly improved by incorporating RCA into HSC, and the improvement depends on the substitution rate of the coarse aggregate. A better shrinkage behaviour can be obtained by raising the substitution percentage of coarse aggregate with RCA; in contrast, the strengths decrease with increased RCA. RCA can be utilised as an internal curing material for HSC to alleviate autogenous shrinkage with a percentage of around 40%, with the adopted ambient conditions in the early age of HSC with full replacement of virgin coarse aggregate. It is recommended to use 24% RCA as a substitution for natural coarse aggregate for internal curing to improve the characteristics of HSC and the sustainability advantages and reduce its negative environmental impacts.

The vast majority of different waste building units have negative environmental impacts around the world. Crushed building units can be recycled and utilized in the concrete industry to solve these problems and maintain natural resources. This study investigated the feasibility of employing crushed autoclaved aerated concrete (CAAC) and crushed clay brick (CCB) as a lightweight aggregate (LWA) to fabricate environmentally friendly recycled lightweight concrete (LWC). In addition, a lightweight expanded clay aggregate (LECA) was also used as an LWA, namely to study how the high porosity of an LWA can adversely affect the properties of LWC. Through the experimental program, all types of LWAs were pre-treated and strengthened with two cementitious grouts, and then the performance of the produced LWC was assessed by determining the slump of fresh concrete, the dry density, the unconfined compressive strength, and the splitting tensile strength at ages of 3, 7, 28, and 56 days. The laboratory results revealed that both CCB and CAAC can be reused as full substitutions for normal-weight coarse aggregate to manufacture LWC with appropriate properties. The obtained data show that the properties of an LECA, CCB, and CAAC were improved, and the porous structure can be strengthened by pre-treatment and coating with grouts. In the same way, the mechanical performance of produced LWC is also enhanced.

Sustainable utilization of polyethylene terephthalate in producing local precast flooring concrete slabs

The aim of current experimental research is to examine the performance of the Reactive Powder Concrete modified by Pulverized Local Wastes materials. In this research, Reactive Powder Concrete was adapted by using local wastes (finely crushed ceramic tiles wastes) with Portland cement, silica fume, water, and chemical admixture through partially replacement of fine sand for sustainable practice in construction. This study exploited normal curing process at ambient temperatures as an alternative of higher temperatures steam curing for sustainability of construction works. To assess the behavior of the modified Sustainable Reactive Powder Concrete mixes, splitting and compressive strengths of Reactive Powder Concrete were inspected experimentally, and then associated with traditional Reactive Powder Concrete mix (the control mix). Furthermore, the hardened density of the modified Sustainable Reactive Powder Concrete was checked. The inquiry results directed that substituting the fine sand partially by Pulverized Local Wastes (finely crushed ceramic tiles wastes) is an adequate method for construction applications. Consequently, the compressive strength and spilling strength of modified Sustainable Reactive Powder were maintained by using 10 % of finely crushed ceramic tiles wastes. Results illustrate that Reactive Powder Concrete have an insignificant strength loss with 10 % sand replacement for compressive strength and splitting strength. The reduction percent in the compressive strength and splitting strength at 28 days are 12.37% and 8.55%, respectively, linked with related control mix.

Reactive Powder Concrete (RPC) is a combined material that will allow the concrete industry to enhance material consumption, produce economic benefits, be more durable, and be more environmentally friendly. Due to the highly dense microstructure of RPC, it performs poorly at high temperatures due to the formation of high pore pressure, which causes material breakdown. This paper demonstrates the outcomes of an investigational study of the behavior of six RPC mixes incorporating hybrid steel and plastic waste (polypropylene) fibers after being subjected to high temperatures of up to 500 ºC. Residual compressive strength, residual splitting strength, and density were performed for all the RPC mixes. The results demonstrate that the drop in the compressive strength of RPC is greater than the reduction in their corresponding splitting strength. Furthermore, within a temperature range of about 500 ºC, this mechanical strength showed a noticeable decrease. The decrement of splitting strength ranged between about 8% to 33% . Steel and polypropylene fibers also improve the residual strength of RPC samples. On the basis of these results, a mix containing mixed fibers (25 % steel and 75 % polypropylene) is recommended as appropriate for extreme temperature applications.