Effect of the Composition of Mixed Recycled Aggregates on Physical–Mechanical Properties

Recycled aggregates (RA) from construction and demolition waste are an alternative to natural aggregates in the construction sector. They are usually classified according to their composition. The main constituent materials are separated into the following categories: unbound natural aggregates, ceramic particles, cementitious particles, bituminous materials, and other materials considered impurities, such as glass, plastic, wood, or gypsum. In this research, a large number of samples of RA were collected from three different recycling plants and their properties were studied. After that, 35 samples were selected randomly, and their RA constituents were separated under laboratory conditions. Cementitious particles were differentiated into two subcategories: masonry mortar and concrete particles. Subsequently, their physical–mechanical properties were measured. The statistical analysis carried out exhibited that the constituents had a statistically significant influence on the physical–mechanical properties studied. Specifically, masonry mortar particles had higher water absorption and worse mechanical properties than concrete and ceramic particles. Secondly, multiple regression models were performed to predict the physical–mechanical properties of RA from their composition since mean absolute percentage error (MAPE) ranged between 0.9% and 8.6%. The differentiation in the subcategories of concrete and masonry mortar particles in compositional testing is useful for predicting the physical–mechanical properties of RA.

Study of the Properties of Full Component Recycled Dry-Mixed Masonry Mortar and Concrete Prepared from Construction Solid Waste

Solutions are needed to solve the problem of a large amount of construction solid waste and a shortage of natural aggregate (coarse and fine aggregates). In this paper, simple-crushed coarse aggregate (SCRCA) and simple-crushed fine aggregate (SCRFA) were obtained by simple-crushing of construction solid waste. On this basis, SCRCA and SCRFA were treated with particle-shaping to obtain particle-shaping coarse aggregate (PSRCA) and particle-shaping fine aggregate (PSRFA), and the recycled powder (RP) produced in the process of particle-shaping was collected. Under the condition of a 1:4 cement-sand ratio, RP was used to replace cement with four substitution rates of 0, 10%, 20%, and 30%, and dry-mixed masonry mortar was prepared with 100% SCRFA, PSRFA, and river sand (RS). The basic and mechanical properties and microstructure of hydration products of dry-mixed mortar were analyzed, and the maximum substitution rate of RP was determined. Under the condition that the amount of cementitious material is 400 kg/m3 and the RP is at the maximum replacement rate, three different aggregate combinations to prepare concrete are the 100% use of SCRCA and SCRFA, PSRCA and PSRFA, and RS and natural aggregate (NCA); the workability, mechanical properties, and aggregate interface transition zone of the prepared concrete were analyzed. The results show that when the replacement rate of RP is less than 20%, it has little effect on the properties of products. The performance of PSRCA and PSRFA after treatment is better than that of SCRCA and SCRFA. Under different RP substitution rates, the performance of dry-mixed mortar prepared with PSRFA is very close to that prepared with RS. The performance of recycled concrete prepared with PSRCA and PSRFA is also very close to that of products prepared with NCA and RS. The failure morphology of PSRCA and RSRFA concrete is also similar to that of NCA and RS concrete.

Effect of Pre-Wetting Recycled Mortar Aggregate on the Mechanical Properties of Masonry Mortar

In this research we evaluated the use of recycled fine mortar aggregate (RFMA) as a fine aggregate for new masonry mortar creation. The pre-wetting effect on the aggregate before creating the mixture was analyzed as a method to reduce its absorption potential. A control mixture of conventional mortar and two groups of recycled mortars were designed with a partial replacement of natural sand by RFMA (pre-wetted and not pre-wetted) performed in different proportions. The results established that the pre-wetting process allows a reduction in the amount of water required during the creation of new mixtures, regulating the water/cement (W/C) ratio and improving the properties of recycled mortars such as air content, fresh and hardened densities, and compressive and adhesive strength for all substitution levels. Mortar made with a 20% substitution and pre-wetted until it was at 67% of its absorption capacity displayed adhesive values higher than the ones shown by the reference mortar. The pre-wetting process proves to be an easy performance technique; it is inexpensive, environmentally friendly, and the most valuable fact is that specialized equipment is not necessarily needed. This process is the most profitable option for improving RFMA exploitation and reuse.

Utilization of Co-Fired Blended Ash and Chopped Basalt Fiber in the Development of Sustainable Mortar

Excessive consumption of cement in construction materials has resulted in a negative impact on the environment. This leads to the need of finding an alternative binder as a sustainable construction material. Different wastes that are rich in aluminosilicates have proved to be a valuable material for alkali-activated product development, which contains zero cement. Alkali-activated products are claimed to be sustainable and cost-effective. In the present study, alkali-activated reinforced masonry mortar was developed using locally available industrial waste (co-fired blended ash—CBA). Appropriate mortar design is one of the key challenges as connections between two structural elements play a significant role in building construction. The mortar designed with suitable fiber reinforcement shall significantly help to enhance the fresh, mechanical, durability, and dynamic properties. Chopped basalt fibers (CBFs) obtained from basalt rock are one of the eco-efficient fibers applied as a reinforcing material. The present study checked the feasibility of novel industrial waste-co-fired blended ash (CBA) in the development of alkali-activated masonry mortar and reinforced alkali-activated mortar. In view of sustainable construction material design, the study elaborated the application of chopped basalt fibers (CBFs) in alkali-activated mortar design. The mortar cubes were cast and tested for various properties with varying percentages of chopped basalt fibers (0.5%, 1%, and 1.5%). The results suggest that developed mortars were able to achieve higher compressive strength (10–18 MPa) and flexural strength (3–3.5 MPa). Further, based on the properties of developed alkali-activated reinforced mortar, masonry prisms were cast and evaluated for the bond strengths (flexural and shear) of masonry. The optimum properties of alkali-activated mortar were found for the mix design of alkali activator to solid ratio of 0.40 and 0.5% CBF percentage. Application of CBF in CBA alkali-activated reinforced masonry mortar proved to be an efficient construction material with no cement.