Search Results (3)

This study investigated the effects of varying water–binder (w/b) ratios and internal curing materials—superabsorbent polymer (SAP) and ceramsite—on the shrinkage behavior and crack resistance of ultra-high-performance concrete (UHPC). Although internal curing has been extensively studied, the comparative effectiveness of different internal curing materials on early-age shrinkage and restrained cracking behavior of UHPC under consistent mixture proportions remains unclear. To address this gap, a systematic experimental comparison of SAP and ceramsite was conducted. The influences of w/b ratio and different amounts and addition methods (dry and pre-absorbed addition) of SAP and ceramsite on the flowability, mechanical properties, early autogenous shrinkage, drying shrinkage, and early crack resistance of UHPC were discussed. Findings indicate that increasing the w/b ratio reduces autogenous shrinkage but compromises mechanical properties, altering the cracking mode from primary microcracks to a few wider cracks. Pre-saturated ceramsite (less than 10% volume) and SAP effectively mitigate autogenous and drying shrinkage, enhancing crack resistance without significantly reducing mechanical properties. However, exceeding a ceramsite volume dosage of 10% or using the dry addition method increased the flowability of UHPC, while decreasing crack resistance. Microstructural analysis reveals that internal curing materials facilitate hydration and enhance structural density through the formation of ettringite and calcium silicate hydrate. To optimize shrinkage reduction while maintaining mechanical properties, SAP should be incorporated in a dry state, with a dosage limited to 0.4% of the mass of the cementitious material; ceramsite needs to be pre-saturated and limited to 5% of the total volume. Full article

To reduce the shrinkage and cracking risk of concrete, internal curing technology was applied to modify concretes with different strength levels (C30 and C60) by incorporating saturated ceramsite. Three kinds of tests were carried out to study the effects of the incorporation of saturated ceramsite on the compressive strength, hydration temperature rise, and shrinkage behavior of the concretes, respectively. It was found that the internal hydration temperature rise of the concrete could be delayed and reduced due to the internal curing effect of ceramsite. Moreover, both the early-stage and long-term constrained shrinkage behavior of the internal cured concretes were monitored with embedded strain sensors and compared with free shrinkage behavior. For the C30 concrete system, with the incorporation of saturated ceramsite, its constrained shrinkage at 96 h was reduced greatly from 181 µε to 36 µε. Furthermore, the surface-attached-sensor method was also used to study the shrinkage behavior of the concrete beams and it was found that the sensor location affected the measured shrinkage values greatly. The model beams of both the C30 and C60 concrete systems shrunk significantly in the first month, and the highest cracking risk occurred in this period as well. The internal curing effect of saturated ceramite could significantly reduce the constrained shrinkage of the concrete beam, evidently diminishing the cracking risk. More importantly, compared to the ordinary concrete C30 system, it was revealed that such an internal curing effect was more effective in promoting the performance of the higher-strength concrete (C60). With this effect, the cracking risk of C60 concrete was reduced from 0.69 to 0.37 at 300 days and changed little from then on. Full article

In rural toilets, black water still remains polluted by nitrogen and phosphorus after being pre-treated by septic tanks. This study uses aerated biofilters to purify black water, screen the biofilter filler, and determine its effect on nitrogen and phosphorus purification in rural black water. This study introduced the concept of the “shape factor” into the Langmuir and Freundlich equations and optimized the isotherm adsorption model to better fit the actual dynamics of nitrogen and purification in black water. Combined with the first-order kinetic equation, the double constant equation, and the Elovich equation, the adsorption performance of seven kinds of biofilter fillers (i.e., zeolite, volcanic rock, sepiolite, ceramsite, anthracite, vermiculite, and peat) was studied. Then, the biofilter was constructed using a combination of fillers with better adsorption properties, and its ability to purify rural black water was studied. Results showed that vermiculite and zeolite had little effect on nitrogen and a high saturated adsorption of 654.50 and 300.89 mg·kg⁻¹, respectively; peat and ceramsite had little effect on phosphorus and a high saturated adsorption of 282.41 mg·kg⁻¹ and 233.89 mg·kg⁻¹, respectively. The adsorption rate of nitrogen from fast to slow was vermiculite > peat > zeolite > volcanic rock > sepiolite > ceramsite > anthracite. The adsorption rate of phosphorus from fast to slow was peat > ceramsite > zeolite > sepiolite > vermiculite > volcanic rock > anthracite. Four combined biological filter fillers aided the removal of nitrogen and phosphorus from rural high-concentration black water. The combination of zeolite and ceramsite filler had a good nitrogen and phosphorus removal effect in high-concentration black water. After the system was stable, the nitrogen removal rate attained 71–73%, and the phosphorus removal rate attained 73–76% under the influent condition of total nitrogen and phosphorus concentrations of 150–162 and 10–14 mg·L⁻¹, respectively. This study provides technical support and reference for the purification and treatment of rural black water. Full article