Chu-Jie Jiao

Properties of recycled aggregate concrete (RAC) are influenced by the composition and particle size distribution of recycled coarse aggregate (RCA). The study herein designed seven distinct groups of RACs with varying aggregate fractal dimensions (D) and one group of natural concrete (NAC). The impact of D on the workability, compressive strength, resistance to chloride ion penetration, and carbonation resistance of RAC was measured. It was found that an increase in the D value led to a decrease in the slump and slump flow, with the compressive strength and chloride ion penetration increasing and then decreasing, and carbonation gradually declined. The optimal fractal dimension was thereby determined to be 2.547 by a strength model accommodating two parameters of D and the curing age. Additionally, the mass percentage of each particle size for the corresponding gradation was presented. The compressive strength and chloride permeation resistance of RAC (D = 1.0) relative to RAC (D = 2.5) was increased by 16.7% and 13.3%, respectively. Furthermore, the carbonation depth of RAC (D = 2.5) was comparable to that of NAC. Additionally, the carbonation resistance of RAC was influenced by both the size distribution and the degree of natural carbonation of RCA, resulting in four distinct features relative to NAC. It is thereby feasible to enhance RAC performance through the manipulation of RCA’s fractal dimensions.

The rising amount of construction and demolition wastes (C & DWs) is triggering serious environmental and social problems globally. This study conducted an experimental investigation of basalt fiber (BF)-reinforced concrete with recycled aggregates (RAs) sourced from C & DWs. The flexural strength, the flexural to compressive strength ratio, and the drying shrinkage are set as indicators for the evaluation of the coupling effect of BF and RA in concrete. Results show that BF generated a significant effect on the flexural strength until the BF dosage was no higher than 1%. The excessive mixing amount of BF, though it still contributed to a positive effect on elevating the flexural strength, was of a reduced utility. Regarding the flexural to compressive strength ratio (denoted as ratio), BF and RA jointly produced a positive synergistic effect. In addition, the BF was verified as competent in curbing the adverse effect of RA incorporation upon the drying shrinkage. Relative to the benchmark concrete which contains 100% RA and no BF, 1% BF contributed to a 31.6% reduction in the drying shrinkage. The results prove that BF reinforcement is a feasible and promising approach to curb the drawbacks of RA concrete.

A photocatalytic mortar containing recycled clay brick powder (RCBP), recycled fine aggregate (RFA), recycled glass (RG), and nanoscale titanium dioxide (NT) was fabricated to degrade low-concentration sulfur dioxide. Instead of intermixing or dip-coating, NT was firstly loaded onto the surface of carriers (RFA and RG) using a soaking method to prepare composite photocatalysts (CPs) denoted as NT@RFA and NT@RG. The prepared CPs can both take full advantage of the intrinsic characteristics of construction wastes, namely, the high porosity and alkalinity of RFA and the light-transmitting property of RG, and can significantly reduce the cost of using NT. RG in high dosage potentially triggers alkali–silica reaction (ASR) in cement-based materials, which affects the durability of the prepared mortar. RCBP, another typical construction waste sourced from crushed clay bricks, was proven to be a pozzolan similar to grade II fly ash. The combined use of RCBP and RG in photocatalytic mortar is expected to simultaneously improve durable performance and further raise the upper content limit of construction wastes. Results exhibit that 70% cement plus 30% RCBP as cementitious material can sufficiently control ASR to an acceptable level. The filling effect and the pozzolanic reaction caused by RCBP result in a decline in porosity and lessened alkalinity, which decreases sulfur dioxide removal. The paper uses both response surface methodology (RSM) and an artificial neural network (ANN) to model photocatalytic efficiency with various initial concentrations and flow rates and finds the ANN to have a better fitting and prediction performance.

Herein, the paper reports an experimental investigation lasting one year on the chloride resistance of polypropylene fiber (PF) reinforced concrete with fly ash (FA). Four influential factors at four levels were studied, viz. water to binder ratio (w/b) (0.53, 0.34, 0.29, and 0.25), PF dosage (0%, 0.06%, 0.08%, and 0.1% in volume basis of the total volume of concrete), FA content (0%, 15%, 25%, and 35% in mass substitution ratio of cement) and concentration of NaCl solution (0%, 3%, 5%, and 7%). Dry–wet cyclic immersion and long-term soaking were taken into consideration in addition to the aforementioned factors. A L16(4⁴) orthogonal table was used to sequence influencing factors and to determine the optimal combination. Results showed that 7% NaCl solution caused the highest chloride content in 0–5 mm depth, whilst the w/b ratio of 0.25 curbed the chloride penetration within 10 mm even for concrete subjected to dry–wet cyclic immersion for 360 d. Subsequently, a respond surface model (RSM) basing on polynomials was constructed to visually evaluate the effect of PF dosage and FA content. Results clarified that a cubic model was more precise and PF dosage and FA content turned out to have the positive facilitation to chloride resistance. The positive effect of PF however is not consistent and commensurate for concrete with varied fly ash content. Finally, a fuzzy logic based nonlinear model accommodating all seven influencing factors was verified to be proper and adaptive in predicting chloride content.