Materials Science Forum Vol. 1036

Abstract: In this paper, the brittleness coefficient, elastic modulus-to-strength ratio, drying shrinkage and autogenous shrinkage and cracking sensitivity were used to investigate the effect of styrene-acrylic emulsion (SAE) on crack resistance of cement-based materials under ultralow water binder ratio (0.22). Then the pore structures, hydration products and surface morphology were also studied to explore the mechanism of SAE on improving the crack resistance of cement-based materials. Results show that, the addition of SAE significantly reduces the elastic modulus, brittleness coefficient, elastic strength ratio, drying shrinkage and autogenous shrinkage of the specimen. The cracking susceptibility is also decreased by the incorporation of SAE and when the dosage of SAE was 5%, the initial cracking time would be extended by 43 hours. In addition, incorporation of SAE can reduce the amount of pores that have an adverse effect on shrinkage, refine the microstructure and decrease the calcium hydroxide formation and microcracks of cement-based materials. Such results would be expected to provide guidance on enhancing the anti-cracking ability of high-performance cementitious materials by the dosage of SAE under low water-binder ratio in practical engineering.

Abstract: In this study, municipal solid waste incineration fly ash (hereinafter called MSWI fly ash) was used as a main raw material, and it was prepared into a solidified body for MSWI fly ash with geopolymer by a single-component chemical alkali excitation method. The results were shown that when the content of MSWI fly ash was 50%, SiO₂/Al₂O₃ was between 3.51-4.04, and Na₂O/Al₂O₃ was between 0.24-0.30, with the increasing of SiO₂/Al₂O₃ and Na₂O/Al₂O₃, the 28d compressive strength of the solidified body showed a trend of increasing first and then decreasing, the maximum 28d compressive strength was 17.7MPa. When SiO₂/Al₂O₃ was 4.04 and Na₂O/Al₂O₃ was 0.30, the minimum leaching concentrations of Pb²⁺ and Cd²⁺ were 0.018mg/L and 0.027 mg/L. When the content of MSWI fly ash was increasing, the 28d compressive strength of the solidified body gradually decreased, and the heavy metal ions leaching concentration gradually increased. The result of XRD and FTIR indicated that the MSWI fly ash was involved in the polymerization reaction, and the heavy metal ions in MSWI fly ash were also chemically solidified into the geopolymer structure.

Abstract: In recent years, with the urgent need of the country to vigorously promote the transformation and upgrading of the construction industry and the modernization of the construction industry, it has been proposed to vigorously develop prefabricated buildings and increase the proportion of prefabricated buildings in new buildings. The prefabricated concrete building is a concrete structure with prefabricated components in the factory and processing and connection on the construction site. Because of its fast construction speed and good overall benefits, it is widely promoted. For prefabricated buildings, the key technology is the connection of structural nodes, and most of the component connections use concrete sleeve connections. The quality of the sleeve grouting material is very important. The basic formula of the grouting material leads to different and different mechanical properties. Conditions apply. This article starts with different sleeve grouting patents, summarizes different functions and characteristics, and provides a reference for the next development of sleeve grouting.

Abstract: The engineering practice shows that the application of grouting technology to treat underground engineering has strong applicability and is one of the most commonly used technical means at present. Based on the underground engineering, this paper introduces the research achievements of grouting materials in recent years, including cement-based grouting materials, mixed grouting materials, anti-scouring grouting materials, and ultra-fine cement grouting materials. Current demand of grouting materials in underground engineering, there exists large dosage of cement, high content, high cost, serious environmental pollution problems, such as looking for alternatives or mixed with other raw materials for preparation of cementation material become the development trend, compared with the cement grouting material, chemical grouting material with higher performance, but in smaller projects within the scope of application. How to reduce the production cost of chemical grouting materials, simplify the production process, overcome the existing toxicity, reduce environmental pollution and improve the durability of solidified body has become the bottleneck of its popularization and application. Some achievements have been made in the modification of cement or chemical materials by nanometer components, but there is still a long way to go before the large-scale application of grouting engineering.

Abstract: Utilizing granulated blast furnace slag (GBFS), coal fly ash (FA), and furfural residue incineration ash (FRIA) as pozzolanic materials, then activated with calcium carbide residue (CCR) respectively to prepare all-solid-waste alkali activated binders (ASW binders). The laboratory tests were performed to research the effects of pozzolanic materials with different reactivity on the macro- and micro- characteristics of solidified marine soft soil. Results show that the mechanical properties and alkali-activation process of ASW binders solidified soil was determined mainly by the reactivity of pozzolanic materials, the higher reactivity of the pozzolanic materials in ASW binders couldn’t change the main hydration products, however, it would accelerate the hydrate reaction. The degree of hydrate reaction increased, the microstructure became denser with the increase of the reactivity of the pozzolanic materials in ASW binders solidified soil, on the macro- side, the strength and deformation modulus of the solidified soil increased, meanwhile, the brittleness of the solidified soil will be more obvious during the deformation resistance process. ASW binders (CCR:GBFS=1:1) solidified soil could reach the strength of cemented soil under the same conditions.

Abstract: Filling grouting is effective to control the overlying strata movement and surface subsidence in mining and tunnel engineering.Grouting material is used in grouting reinforcement projects. In this experiment,based on the mechanical properties of grouting materials, Expert Design and response surface methodology (RSM) is used to optimize the mix proportion of grout materials. The sand-fly ash ratio ,water reducing agent addition are researched as variables, and the 3D response surface is established between the factors and the performance indicators. Microstructure explains the mechanism of factors affecting performance indicators.The results show the relationship between factors and performance can be well fitted by RSM.The order of significance on compressive strength and solidification ratio is sand-fly ash ratio＞water reducing agent addition and the order of significant on viscosity is water reducing agent addition＞sand-fly ash ratio.Response surface methodology accurately describes the functional relationship between the target value and the design variables.Microstructure shows hydration reaction and the secondary hydration reaction of fly ash will be carried out after cement-fly ash mixed, and the addition of fly ash is especially important for grout material properties.

Abstract: The carbonation process in alkali-activated slag cement concrete is more complicated. This paper reviews the research progress of carbonation resistance of alkali-activated slag cement concrete at home and abroad and summarizes the existing research on carbonation. The focus is on the carbonation mechanism, test methods, influencing factors and the effect of carbonation on the performance of alkali-activated slag cement concrete. The problems existing in the current research on the anti-carbonation property of alkali-activated slag cement concrete and the issues for further research are proposed.

Abstract: Chloride ions, water, and oxygen could cause the corrosion of steel fiber in the aggressive environment. The corrosion of steel fiber in UHPC is a long-term process and the rate is very slow. As one of the important components of ultra-high performance concrete (UHPC), the corrosion of steel fiber is the result of multiple factors. The characteristics of steel fiber corrosion in UHPC, the factors influencing the corrosion of steel fiber in UHPC (including nanomaterials, curing condition and crack width), and effects of steel fiber corrosion on the UHPC performance (including mechanical properties, matrix rehydration and corrosion of steel bar), are emphatically elaborated. And the control methods of steel fiber corrosion in UHPC are briefly introduced, i.e. hybrid fibers and stainless steel fibers.

Abstract: In this paper, the influence of liquid alkali-free accelerator and advanced composite cementitious materials on the mechanical properties, durability and workability of shotcrete was studied. The important role of the two materials in the performance improvement of shotcrete was clarified. The technical measures proposed were verified by field test. The results show that: In terms of workability, the composite use of alkali-free accelerator and functional admixture can achieve fast setting and high early strength of shotcrete, thus effectively reducing the rebound rate; In terms of mechanical properties, functional admixture can effectively improve the early mechanical properties of shotcrete, while alkali-free accelerator can ensure the long-term development of mechanical properties; In terms of durability, the use of functional admixtures can effectively improve the compactness of shotcrete, and the test results of 56d electric flux are lower than 1000C.

Abstract: Alternating-current method for measuring chloride penetration resistance of concrete, test method for coulomb electric flux and rapid chloride migration coefficient (RCM) were applied to evaluate the resistance of chloride penetration in alkali-activated slag concrete in this paper. At the same time, the applicability of the above three electrical parameters test methods to the alkali slag concrete was discussed. The results show that NaOH activated slag concrete behaves higher resistance to chloride penetration than water glass activated slag concrete. Blend of fly ash increases the porosity of alkali-activated slag concrete and weakens the resistance of chloride penetration. Correlation coefficient between chloride migration coefficient and AC electrical resistivity is 0.99. There are good correlations among the evaluation results of three electrical parameters test methods, and all of them behave sound applicability to alkali-activated slag concrete.