The effect of heat treatment of Fly ash (FA) on the properties of reinforced cementitious materials was investigated. The glass phase content of FA was evaluated after heat-activated their pozzolanic activity through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Scanning electron microscope (SEM) methods. The mechanism of heat-activated FA reinforced cementitious materials was reveled from the mechanical properties of fly ash-cement (FA-OPC). The results show that the glass phase content of FA gradually increased as the heat-activated temperature rises. The microstructure and the elemental composition of on the surface of FA particles after heat treatment proved the existence of an inert oxide layer on the surface of FA spheres, which affected the release of active substances in the glassy network structure of FA. However, the cementitious activity decreased with increasing heat treatment temperature when used in FA-OPC. Compressive strength decreased after hardening, which was consistent with the micro-morphology observation by SEM.

Although there have been many research results on the chemical activation of fly ash (FA) as a supplementary cementitious material (SCM) in cementitious materials. However, there is a lack of research on the use of CO2 foaming agent (sodium bicarbonate and potassium aluminum sulfate) to activate fly ash. In this experiment, the effects of CO2 foaming agent, sodium bicarbonate, and potassium aluminum sulfate on the activity of FA mixed paste were investigated. The mechanism of FA activation by activator was revealed by selective acid dissolution, QXRD, BSE-EDS statistical analysis, and quantitative analysis of TGA. The results showed that the remaining fly ash amounts of MG, SBG, and PASG after 28 days were 17.5%, 25.9%, and 43.3% lower than those of the control group, respectively. In addition, potassium aluminium sulphate promoted hydration to generate more CH to activate the FA. Sodium bicarbonate promoted hydration and produces more CH to activate FA by generating nano-CaCO3. The mixture of sodium bicarbonate and potassium aluminum sulfate took advantage of both nano-CaCO3 and potassium aluminum sulfate to promote silicate hydration to provide CH. As a result, the two syn-ergistically activate FA. The above results show that CO2 foaming agents can be used not only as foaming agents to prepare lightweight materials, but also as chemical activators to activate solid waste. This will have a high practical application value.

Coal mine filling requires a safe, lightweight, and high-strength filling material, but current commonly used aeration agents, such as hydrogen peroxide, which produces the combustible gas O-2, and aluminum powder, which produces the explosive gas H-2, are not suitable for coal mine filling. In this paper, a new inorganic composite aeration agent, namely sodium bicarbonate and potassium aluminum sulfate, which produces inert gas CO2, was developed. The effects of this composite aeration agent admixture (at contents of 0%, 2%, 4%, 6%, and 8%) on the properties such as fluidity, setting time, compressive strength, and water resistance of sulfoaluminate cement paste with high water-to-cement ratios were investigated systematically. The evolution of the microstructure and pore structure of this foamed material was determined using X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), and scanning electron microscopy (SEM). The results showed that when the amount of aeration agent was 8%, the 7-day compressive strength of the prepared sulfoaluminate cement-based foamed material with a dry density of 600 kg/m(3) was 1.2 MPa. Compared with the control group, the setting time was shortened by 87%, dry density was reduced by 42.1%, 7-day compressive strength was increased by 47.5%, and water resistance was increased by 45.4%. The composite admixture not only formed uniform bubbles within the sulfoaluminate cement paste but also produced in situ calcium carbonate, which promoted the hydration of sulfoaluminate cement and made the microstructure of the hardened paste denser. The results provide new materials for coal mine foam filling, which can be applied to corner gas control and foam filling in mining areas and coal mine fire prevention.

In our previous work, an in situ wet carbonation method was proposed to enhance the activity of waste-sintering red mud (SRM) by producing large amounts of fine calcium carbonate and silica-aluminum gels. This paper further investigates the effect of carbonated SRM (C-SRM) dosing (0%, 5%, 10%, 15%, 20% and 25%) on the hydration-hardening properties of sulphoaluminate cement (CSA) clinker paste, such as flowability, setting time, reaction temperature, compressive strength, microstructure and pore structure evolution. The results show that the use of C-SRM as a new mineral admixture not only significantly improves early strength but also effectively compensates for the strength deficit of CSA clinker due to the conversion of AFt to AFm at a later stage. When the C-SRM content is 20%, the compressive strength reached its maximum at all ages, with the 1 d compressive strength increasing by 96.9% and the 90 d compressive strength by 19.8%. The microstructure analysis shows that the C-SRM has a good crystalline nucleation effect and can participate in the hydration reaction of CSA clinker, forming semi-carbonate aluminates and stabilizing ettringite, thus densifying the microstructure of the hardened paste. The above results open new possibilities for incorporating C-SRM as a novel mineral admixture into CSA clinker while further reducing CO2 emissions.

Polymer-modified cementitious materials with high compression and tensile resistance are considered the most promising materials for fracture grouting in underground projects. In this paper, polyacrylamide was prepared by in-situ polymerization of acrylamide, and its toughening effect on sulfoaluminate cement-based grouting material (SCGM) was investigated. The results show that the toughness index of the acrylamide modified SCGM (PAM-SCGM) was 57.55 times higher than that of the plain one. The PAM-SCGM three-stage failure model and the PAM-AFt-CS dual network structure model were proposed and validated by SEM. A model of PAM inhibition of hydration was proposed and validated using heat of hydration, FT-IR and XRD. BET was used to reveal the evolution of the pore structure and validated the tensile model. An empirical formulation of a three-stage mechanical model was proposed and regressed to validate it. The four models and an empirical formulation showed the great potential for engineering applications.

During the process of rapid repair, the Portland cement-sulphoaluminate cement clinkeranhydrite-fly ash quaternary system exhibited weak toughness, low flexural strength, and low compactness. To solve these problems, this paper modified the quaternary system by acrylamide (AM) in-situ polymerization and investigated the effects of different AM content (0%, 2%, 3%, 4%, 5%, 6%) on the macroscopic properties of the quaternary system, such as flowability, setting time, and mechanical properties. The enhancement mechanism of the toughness and the microstructure evolution of the quaternary system was revealed by XRD, TG-DTG, FT-IR, SEM, and other tests. The results showed that the addition of AM could improve the flowability and the flexural strength of the quaternary system in the late stage, and the flexural strength of the cement specimens increased by 14.81% and 26.83% at 7 d and 28 d, respectively, when the AM dosing was 4%. Meanwhile, the toughness and flexibility of the quaternary system were also improved. The inorganic-organic interpenetrating network structure formed by the in-situ polymerization of PAM and hydration products allowed more energy to be absorbed before the damage, thus improving the overall toughness. Furthermore, PAM can form a perfect mesh structure in the cement slurry, which not only connects the AFt crystals but also acts as a bridge, which facilitates its later flexural strength improvement. The above results expand the application of the polymer in cement-based materials, effectively alleviate the stress damage of cement materials during the repair process, and further promote the application of the quaternary system in the field of rapid repair engineering.

High-risk areas in coal mines have become an increasingly serious issue in recent years. However, the chemical foaming agents used in coal mine filling management are mostly hydrogen peroxide which produces combustible O2 and aluminum or zinc powder which is explosive H2. All of the above chemical foaming agents do not have safe filling conditions. In this paper, we propose a new inorganic foaming material that generates inert gas CO2. Foamed sulfoaluminate cement-based grouting material (FSCGM) was prepared by chemical foaming. The expansion capacity of CO2 foaming agent was studied. The effects of W/C, foaming agent admixture, and Lime/Anhydrite (L/A) on expansion times, foaming time and setting time were studied and the optimum proportion of FSCGM was determined. The mechanical properties, durability, and fire prevention performance of the FSCGM with the optimal proportion were studied and simulated filling tests were conducted. The results showed that the CO2 foaming agent with 30% dosing expands 8.8 times after 10 min of foaming. The best proportion of W/C was 2.2, CO2 foaming dosing was 25%, L/A was 3:5, 6 h compressive strength was 0.52 MPa, 7 d water absorption rate was 46.2%, softening coefficient was 0.75. With the increase of foam admixture and W/C, the CO2 concentration gradually increased, and the fire prevention effect became more apparent. After simulated filling, the slurry did not collapse the mold, the expansion times was 1.74 times, and the dry density of the sampled specimens was about 0.3 g/cm3. It is observed that the bubbles were evenly distributed, and the hole structure was small and dense. Therefore, we prepared FSCGM with ultra-low density, high early compressive strength, and good fire prevention performance by using novel CO2 foaming agent. In addition, the feasibility results indicate that the FSCGM has great potential for engineering applications.

A safe, lightweight, inexpensive, quick-setting filling material is needed for high riser areas in coal mines. However, currently commonly used foaming agents, such as hydrogen peroxide, which produces the combustion gas O 2 , and aluminum powder, which is explosive gas H 2 , are not suitable for coal mine filling. Therefore, a new composite foaming agent that produces CO 2 , namely sodium bicarbonate and potassium aluminum sulfate, was proposed. The effects of CO 2 foaming agent dosing on the fluidity, setting time, compressive strength, water absorption, and dry density of OPC-CSA-FA ternary composite paste filling material (CPFM) were systematically investigated. The hydration mechanism and pore structure evolution of the foamed filling materials were revealed by XRD, TG-DTA, SEM, etc. The results showed that CPFM blocks with a 28-day dry density of 790 Kg/m 3 , compressive strength of 2.73 MPa, and water absorption of 25.8% were prepared when the CO 2 foaming agent was dosed at 10%. Compared with the control group, the setting time was shortened by 92.5%, the 28-day compressive strength was increased by 28.1%, and the 28-day water absorption was reduced by 48.3%. The addition of a small dose of CO 2 foaming agent not only excites the fly ash activity and generates hydrocalumite and para-alumohydrocalcite, which are beneficial to the strength, but also a large amount of generated aragonite and nano calcite promotes the hydration and fills the pores to form a more dense microstructure. The above research provides new materials for foam filling management in high riser areas of coal mines.

为降低超高性能混凝土(UHPC)黏度、提高工作性,采用硅烷(γ-缩水甘油醚氧丙基三甲氧基硅烷、十二烷基三甲氧基硅烷)对辅助胶凝材料(硅灰、粉煤灰)进行改性制备了自分散颗粒,并研究了其对UHPC工作性、抗压强度及微观结构的影响.结果 表明:自分散颗粒降低了UHPC的黏度,提高了工作性;不同自分散颗粒对UHPC工作性的影响有较大差别,其中,粉煤灰和十二烷基三甲氧基硅烷制备的自分散颗粒效果最好;自分散颗粒抑制胶凝材料的早期水化,降低UHPC早期抗压强度;不同自分散颗粒对UHPC的28 d抗压强度影响也各不相同,采用粉煤灰和十二烷基三甲氧基硅烷制备的自分散颗粒提高了UHPC的28 d抗压强度,其他自分散颗粒降低了28 d抗压强度.