Papers by Keyword: Cementitious Materials

Abstract: Experimental techniques like X-ray diffraction (XRD) and pore size distribution determination (MIP), in conjunction with thermodynamic simulation (GEMS) and kinetic modeling of cement hydration (PK), were used to analyze the microstructures and phase compositions of cementitious materials under the coupling effect. This allowed researchers to study the evolution of formation products and pore structure of cementitious materials under the coupling of long-term wet and dry cycling and sulphate erosion. The findings demonstrate that the cement pastes with varying w/b ratios formed the expansion products calcium alumina and gypsum after 180 days of dry and wet cycling by 5% sodium sulphate solution; however, the specimens with lower water-ash ratios had denser structures, fewer erosion products, and better resistance to sulphate erosion. The following illustrates how sulphate erosion products affect the pore structure: during the early stages of erosion, the pore structure becomes more refined and has an increase in the number of transition pores between 10-100 nm due to the erosion products such calcium alumina and sodium sulphate crystals filling the pores. The degree of sulphate erosion is exacerbated by the formation of new cracks and larger macropores, which result in an increase in the number of erosion products, an increase in the average pore size, and a looser pore structure. However, the calcite growing in the transition pores is more destructive, and the crystallisation pressure keeps building up, leading to the destruction of some of the transition pores.

Abstract: The present study evaluated the engineering properties and microstructure of an alternative binder composed of calcium carbide residue and silica fume. The cementitious mechanisms of this alternative binder based on the pozzolanic reaction in raw materials. The ratio of calcium carbide residue and silica fume was decided based on the chemical composition of raw materials and their chemical reaction. The calcium carbide residue-silica fume mortar was prepared and tested for its compressive strength at several curing periods, with results then compared to conventional mortar made with ordinary Portland cement. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate the microstructure of hardened mortars. The test results suggest that the compressive strength of calcium carbide residue-silica fume mortar continuously developed throughout the curing period. The relative compressive strength of calcium carbide residue-silica fume mortar reached 72.78% of the ordinary Portland cement mortar strength at 28 days curing age.

Abstract: The development of new environmentally friendly binder from calcium carbide residue and fly ash wastes were investigated in this study. The key point of this work is difference to several previous investigations in that the optimized mixture proportion of the raw materials were calculated based on their chemical composition and their reaction. The compressive strength development over the curing age was also compared with reference mortar created with OPC binder. Mortar cubes were cast from the mix containing the calcium carbide residue and fly ash, at the optimized ratio. The compressive strength of the mortar was then monitored over an extended period: at 56 days it was 10.66 MPa, which is approximately 47% of the reference mortar. The morphologies and chemical compositions of the developed mortar showed the presence of spherically shaped of unreacted fly ash powder particles embedded in a cement C–S–H gel resulting from the pozzolanic reaction of raw materials.

Abstract: 3D construction printer - is an innovative construction approach with which building elements can be constructed without the use of formwork and you to get products of various complex shapes with minimal time and material costs. Binder 3D printing technology results in a cheap and high-speed construction method that allows greater freedom in both architectural and structural design of concrete. The principle of operation of a 3D printer is based on the principle of gradual (layer-by-layer) creation of a solid model, which is, as it were, "grown" from a certain binding material. The working mixture must have thixotropic and adhesive properties, it must be workable by the printer and at the same time not spread under the influence of subsequent layers. Therefore, it is important to select the composition of the composition of the working mixture. This paper presents the results of a study on the development of the composition of a working mixture based on a gypsum-cement-pozzolanic binder. The developed composition of the gypsum-cement-pozzolanic binder with a complex of modifying additives is characterized by low spreadability, high viscosity and is easy to lay.

Abstract: In this paper, several urea–formaldehyde/epoxy microcapsules with different particle sizes were synthesized by in-situ polymerization. The chemical structure and compressive rupture load of microcapsule were characterized. The effect of microcapsule dosage, particle size and preload pressure on compressive strength of cementitious materials was studied. The result shows: when the particle size of microcapsule is 2 mm~2.5 mm, the rupture load of microcapsule is highest, more than 3N; When the microcapsule dosage is less than 2.5%, the strength loss of the matrix is relatively small; With the increase of the particle size of the capsule, the strength of the matrix decrease greatly; When the dosage of microcapsule is 2.5%, the particle size is 1.5 mm and the preload pressure is 30%~45%f_max, the compressive strength of the self-healing specimen is 8% higher than that of the non-preloaded specimens, which shows a certain self-healing performance.

Abstract: There are significant changes observed in concrete materials, the properties of innovated concrete have also experiencing revolutionize through hi-tech encroachment. Instead of new changes in the materials used in concrete making, the adjustment in concrete is started from conventional concrete strength and slowly tracked by high-strength concrete and high-performance concrete. Recently, the exploitation of by-products waste in the self-compacting concrete (SCC) had achieved massive interest among researchers due to practicable and beneficial features. Most of the prior works focused on SCC combining with supplementary cementitious materials such as fly ash, coal bottom ash, silica fume, ground granulated glass blast-furnace slag and rice husk ash. Concrete with these cementitious materials have been used extensively throughout the world. These materials used as mineral admixtures in concrete and strengthen the durability and concrete properties. The concrete applications are increasing with the passage of time due to their superior structural performance, environmental friendliness and low impact on energy utilization. Through these understanding, this research points out the idea of cementitious materials in concrete, especially SCC possess with numerous positive features such as durability, flowability and overall performance of concrete. It can be seen that cementitious materials have high benefit and lead to curing potential. However, it is important to understand that these materials are relatively expensive. Thus, this is a main reason behind their less adoption compared to add as mixtures in Portland cement.

Abstract: This study is aimed to evaluate the tensile strength and impact resistance of cementitious materials which comprise steel fibers and silica fume in the mixes. Material variables include water-binder ratio, dosage of silica fume, steel fiber length and dosage. A designed tensile strength was used to perform the direct tensile in this study. Test results indicate that the compressive strength, splitting tensile strength and direct tensile strength of specimens for fiber length of 60 mm are higher than that of 35 mm. The inclusion of fibers in specimens containing silica fume has higher compressive and tensile strength; and lower impact resistance than the specimens made with silica fume. Incorporation of steel fiber and silica fume in composites achieves significantly higher increase in compressive strength, splitting tensile strength, and direct tensile strength than only individual use of steel fiber or silica fume and decrease in impact resistance than only individual use of steel fiber. Finally, the proposed direct tensile testing method is suitable for determining the tensile strength of fiber reinforce cementitious materials and generating the tensile stress-strain curves easily.

Abstract: The objective of this study is to realize a non-destructive characterization of cementitious materials using ultrasonic method. The motivation of our work is to show that the ultrasound can be applied not only in medical imaging but also in the assessment of construction materials, which is not widely known in this domain. In order to solve the problem, the ultrasonic velocity measurement was performed on the samples before and after carbonation of a standardized mortar at different periods. The results offer the possibility to determine the mechanical properties such as Young modulus E, shear modulus G and Poisson's ratio. This is an advantage for in-situ structures in comparison with destructive methods that require destroying the samples. The main contributions of this study are: 1) Ultrasonic occultation of cement materials is a reliable method with a small margin of error; 2) The values ​​of mechanical properties found by ultrasonic method are consistent with theoretical values ​​found in the literature; 3) The evolution of these mechanical properties is consistent with the densification of the microstructure during carbonation due to the formation of CaCO₃.

Abstract: The back-filling method is distinguished from other mining methods by its higher cost. In order to solve this problem and utilize water-granulated nickel slag as much as possible, nickel slag from flash smelting operation was used to prepare cementitious materials for backfilling. Approaches including mechanical activation and chemical activation were adopted to improve the cementitious activity of the slag. By taking the strength of the backfill materials as the evaluation standards, the hydration activity and cementitious performance of the slag were investigated under different activation conditions, and the mechanism of chemical activation was analyzed. The results shows that cementing agent prepared by using mainly the slag (occupying 85% of the total raw materials) can be used to replace cement and meet the production requirements for backfilling materials.

Abstract: Microstructural properties have been studied in cementitious materials, which were subjected to cyclic sulfate exposure, through x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and mercury intrusion porosimetry (MIP). Results indicate that portlandite in OPC concrete and OPC-FA concrete is mainly converted to gypsum. Portlandite in OPC-GBFS concrete is mainly converted to gypsum and ettringite. Concrete subjected to the cyclic sulfate attack has a lower porosity and the higher amount of macro-pores than that before exposure. Concretes incorporating FA or GBFS had lower porosity and higher amount of micro-pores than OPC concrete.