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Brittle fracture is a typical mechanical characteristic of high-strength self-compacting concrete, and the research on its toughening modification remains the highlight in the engineering field. To understand the effect of toughening materials (including polymer latex powders, rubber particles, and polyethylene fibers) on the mechanical behavior of C80 high-strength self-compacting concrete under static loading, the failure mode, mechanical strength, strain field, and crack opening displacement (COD) of prepared high-strength self-compacting concrete under compressive, splitting, and flexural loads were studied based on digital image technology (DIC). The corresponding mechanism is also discussed. The results show that the hybrid of polymer latex powders, rubber particles, and polyethylene fibers can increase the crack path and inhibit the development of macrocracks in concrete, thus turning the fracture behavior of concrete from brittle to ductile. The addition of toughening materials reduced the compressive and flexural strengths of high-strength self-compacting concrete, but it increased the splitting strength. DIC showed that the incorporation of toughening materials promoted the redistribution of strain and reduced the degree of strain concentration in high-strength self-compacting concrete. The evolution of COD in high-strength self-compacting concrete can be divided into two stages, including the linear growth stage and the plastic yield stage. The linear growth stage can be extended by incorporating toughening materials. The COD and energy absorption capacity of concrete were enhanced with the addition of toughening materials, and the best enhancement was observed with the hybrid of polymer latex powders, rubber particles, and polyethylene fibers. Overall, this research provides a reference for exploring effective technical measures to improve the toughness of high-strength self-compacting concrete.

In this research, the electrolytic manganese residue (EMR) based belite-ye'elimite-ferrite (E-BYF) clinker composed of 51.6 % belite, 25.6 % iron phase, 15.8 % ye'elimite and 6.5 % over-burned anhydrite phase was manufactured successfully at 1200 °C _ 30 min by utilizing EMR (45.5 %) and additional CaO and Al2O3. The existence of iron-rich and heavy metal phases was a potential driving force for achieving near complete calcination at 1200 °C _30 min. The iron ions (8.4 %) and the over-burned anhydrite phase partially replaced the Al3+ ions by entering the ye'elimite lattice and provided enough SO3 (5.9 %) to help stabilize ye'elimite and β-C2S formation, respectively. Layered double hydroxides such as AFm phase and strätlingite formed dense microstructure and improved pastes strength as a new rigid skeleton. The formation of rigid solid skeleton-flexible gel embedded co-support system provided a reliable solution for eliminating inherent strength plateau (3-day of 45.9 MPa and 60-day of 107.0 MPa). In this system, the solid-phase hydrates as the main skeleton offered sufficient rigid-supporting, while the gels hydrates as the auxiliary fluid that filled into the pores of the formed skeleton gave the adequately flexible-supporting. In addition, the pastes showed an excellent stabilization ability of heavy metals. The E-BYF system has great potential in reducing CO2 emissions (0.58 kg/kg and 1.36 kg·/MPa·m3) and cost. This work provides a new perspective for a high-quality solution to the strength plateau while achieving a high value-added utilization of EMR.

Developing an eco-friendly UHPC with Belite cement (BC) is a great challenge because the mechanical strength of concrete with BC develops much more slowly than Ordinary Portland cement (alite-rich cement, OPC). However, BC has a lower CO2 footprint than OPC due to a lower calcined temperature and less limestone demand, making it green cement. Besides, concrete with BC has better long-age performance. In this study, the utilization of BC in UHPC was compared to that of OPC. Three curing regimes were used for the designed UHPC. The compressive and flexural strengths of UHPC-BC are lower than of UHPC-OPC at one day but higher after 28 and 90 days of standard curing. After heat curing, the mechanical strength development of UHPC-BC improves noticeably and exceeds UHPC-OPC. UHPC-BC has a higher flexural strength to compressive strength ratio (ff/fcu), and there are more C–S–H, less CH and lower pore coarsening of UHPC-BC paste than UHPC-OPC, especially after heat curing. UHPC-BC has lower environmental impact indices at long age than UHPC-OPC. At 90 days of autoclaved curing, the compressive of UHPC-BC reaches up to 197.5 MPa with the embodied carbon content of 934.37 kg/m3, which is much lower than most UHPCs.

In this work, manganese tailing sand concrete (MTSC) was prepared using manganese tailing sand (MTS) in replacement of river sand (RS) to alleviate the shortage of RS resources and achieve clean treatment and high-value resource utilization of manganese tailing stone. The effects of MTS content on the slump, mechanical strength, air void characteristics, hydration products and micromorphology of MTSC were studied experimentally. The leaching risk of harmful substances in MTSC was also explored by testing the concentration of Mn2+. The results show that the utilization of MTS reduces the slump of MTSC to a certain extent. When the MTS content is lower than 40%, the gypsum introduced by MTS and C3A in cement undergoes a hydration reaction to form ettringite, which decreases the number of pores with a diameter less than 0.1 mm and promotes strength development in MTSC. Additionally, when the MTS content exceeds 40%, the large amount of gypsum reacts to form more ettringite. The expansive stress generated by the ettringite severely damages the pore structure, which is not conducive to the mechanical properties of MTSC. In addition, the leaching of hazardous substances in MTSC is insignificant, and the incorporation of cement can effectively reduce the risk of leaching hazardous substances in MTSC. In summary, it is completely feasible to use MTS to replace RS for concrete preparation when the substitution rate of MTS is less than 40%, with no risk of environmental pollution. The results and adaptation in the concrete industry can reduce the carbon footprint, which is in line with the current trend in civil and materials engineering.

To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste, several measuring methods including X-ray diffraction (XRD), atomic absorption spectroscopy (ASS), ion chromatography, conductivity meter, alternating-current impedance spectroscopy and nuclear magnetic resonance (NMR) are employed to investigate the hydration characteristics, pore solution composition and conductivity, resistivity and pore structure during the steam curing process. Experimental results show that steam curing promotes the hydration process, greatly raises the resistivity, and decreases the porosity of specimen at early age. Compared with being treated at 45 °C, higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period, which improves the relative content and ionic activity of the conductive ions in pore solution. Furthermore, the number of pores larger than 200 nm increases significantly, which reduces the resistivity of the hardened cement paste. Cement paste treated at 45 °C has a more stable and denser microstructure with less damages.

The self-compacting concrete (SCC) filling layer is a key structural component of the China railway track system type III ballastless track structure. The quality of the filling layer directly affects the durability, comfort and safety of the track system. Based on job site practice in the construction of the Zhengzhou–Fuyang high-speed railway, the distribution characteristics of the dynamic elastic modulus and homogenisation index of the SCC used as the filling layer with different workability parameters (slump flow, T500 and filling time) were obtained by sampling the SCC core from the filling layer. Image analysis software was employed to analyse the size and distribution characteristics of the surface defects statistically. The filling layer quality was evaluated according to the homogenisation index and the surface defect ratio. The results showed that the dynamic elastic modulus of the SCC in the filling layer tended to decrease from the intermediate filling hole to the four outlets. The order of influence of workability parameters on the filling layer quality was found to be T500, slump flow and filling time.

The low reactivity of fly ash (FA) restricts its application in concrete. To promote the utilization of FA, the research on the activation of FA has been one of important hotspots in related fields...

The direct stockpiling of electrolytic manganese residues (EMR) poses a major environmental issue, and more eco-friendly disposal is urgently needed. The combination of cement solidified waste (CSW) and direct electric curing (DEC) provides a potential solution for hazard-free value-added utilization of EMR. The effects of DEC voltages and EMR dosages on mechanical properties, hydrated products, pore structure of mixture were investigated. The influencing mechanism of DEC on the properties of cement hydration was explored in-depth using TG and XRD results. The environmental and economic evolution of DEC was analyzed, and the leaching test was conducted to evaluate the immobilization of heavy metals. Results indicate that cement-EMR pastes cured in higher DEC voltage and reduced EMR dosage increase mechanical strength and improve pore structure and capillary water absorption with respect to indoor curing (IC). The increased cement dosage improves the effectiveness of CSW, while the increased DEC voltage enhances the ionic driving force. The boosted ettringite formation occurs in system after introducing DEC and amplifying the DEC voltage. The improvement of ion concentration in DEC accelerates the formation of hydration products. The CO2-e per MPa (EIF) and cost per MPa (CIF) values of paste DMP-7 cured in 12V-DEC exhibit the lowest values with respect to those cured in other voltages and IC. The decrease in the leaching amount of Mn2+ and NH4+-N as the DEC voltage increases, and the 28-d leaching concentration of Mn2+ and NH4+-N in pastes are in accordance with the national standards. The application of DEC and cement-solidified disposal for EMR could provide a potential solution for high-value and large-capacity disposal of hazardous solid waste.

Supplementary cementitious materials have significant potential to reduce greenhouse gas emissions in the production of construction materials. This work investigated the synergistic effect of partially replacing cement by sewage sludge ash and limestone for sustainable cementitious material production. The hydration phases and pore structure characteristics were determined by X-ray diffraction and the BET nitrogen sorption method, respectively. A central composite rotational design (CCRD) was used to study the effect of the water binder ratio (w/b), sludge ash and limestone content on the compressive strength. The results of microstructure tests showed that the addition of limestone enhanced the formation of carboaluminate hydrates. The additional hydration products filled in large pores of paste, resulting in a well-refined microstructure of the ternary mixture. Thus, the 90-day strength activity index (SAI) of mortar with 15% sludge ash and 7.5% limestone was 100.6% compared to the reference. Despite the adverse effect of limestone on the compressive strength, the synergistic effect of sludge ash and limestone contributed to the reduction of economic cost and greenhouse gas emission in the production of sustainable cementitious materials. For the same compressive strength level, the ternary mixture composed of 15% sludge ash and 7.5% ground limestone reduced Portland cement consumption by 23.13% and CO2-eq emission intensity by 13.52%.

As a high-output industrial byproduct, fly ash can partially replace Portland cement in concrete, which is one of the important treatment methods to improve its utilization. However, the low activi...

In order to investigate the deterioration mechanism of steam-cured concrete under severe environmental actions such as acid rain corrosion, salt corrosion, and cyclic thermal loading, accelerated corrosion tests were conducted in this study. Surface damage as well as deteriorative kinetics of steam-cured concrete and cement paste suffering from coupled acid-thermal actions was investigated by soaking-drying cycle experiments. The effects of mineral admixture, curing regime and corrosion condition on the durability were all comparatively studied, and the X-ray diffractograms and nanoindentation were applied to analyse the mechanism of corrosion deterioration. The results revealed that compared with the cementitious materials under standard curing, larger depth and faster corrosion were observed for steam-cured concrete and cement paste, which might be partly attributed to the lower content of hydrated production presented in steam-cured specimens. Besides, under acid solution soaking-drying cycle regime, there was significant higher corrosion depth compared to only soaking in acid solution. The corrosion depth under steam curing and soaking-drying condition increased by 156.68% and 44.17%, respectively, compared with those under standard curing and only soaking treatment. In addition, fly ash effectively decreased the corrosion depth of steam-cured cement paste and concrete by 64.98% and 16.33%, respectively.

In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and double-layer board with gradient structure. The mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with the appropriate mix proportion exhibited the almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3MPa and 1MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and explore the mechanism of sound absorption and insulation in the material.

Sewage sludge ash has potential to be used as supplementary cementitious material in the production of building materials. The chemical effect of sewage sludge ash on early-age hydration of cement was investigated in this study. Two types of sludge ash calcined at 600 °C (S600) and 800 °C (S800) were blended with cement for analysis of hydration heat evolution, solid phase assemblage and aqueous composition. The aluminate dissolution of S600 ash promoted the formation of ettringite and consumption of gypsum, resulting in a high initial hydration heat. However, high concentrations of Al and Si caused by continuous dissolution of aluminate and silicate in S600 ash inhibited significantly the C3S dissolution. Interestingly, S800 ash had slight effect on early cement hydration since higher calcination temperature decreased the activity of aluminate. As compared with the reference, cumulative hydration heat of blended paste with 30% S800 ash at 7 days was increased by 18.72% indicating the occurrence of reaction between sludge ash and cement. Further study is recommended to focus on the long-term performance of cement-based materials blended with sludge ash.

The application of aluminum-based flocculant in wastewater treatment results in a large amount of aluminum-rich sewage sludge. This work investigated the influence of calcination process on physicochemical characteristics and pozzolanic activity of aluminum (Al)-rich sludge ash and studied the effect of sludge ash on cement hydration. The results showed that higher calcination temperature from 600 ℃ to 900 ℃ increased the amorphous content in sludge ash. The pozzolanic activity of sludge ash calcined at 800 ℃ and 900 ℃ was confirmed by Frattini test. In view of strength activity index of blended mortar and energy conservation, the optimal calcination condition of sewage sludge ash was calcined at 800 ℃ with air-cooling. The addition of sludge ash promoted the transformation of ettringite to monosulfate phase in cement paste. However, the high Al concentration dissolved from S6 and S7 ash inhibited significantly the cement hydration and resulted in low compressive strength values of the blended mortars. The pozzolanic reaction of S8 and S9 ash produced more hydration heat and additional Al-bearing products such as katoite and monosulfate which contributed to the strength development of mortars. Furthermore, the heavy metals in sewage sludge can be immobilized in ash structure during calcination process and the structure of hydration products, which ensures the environmental security of sludge ash utilization in construction materials.