Shuhua Liu

Effect of curing temperature on hydration properties of waste glass powder in cement-based materials

The effect of curing temperature on the hydration properties of waste glass powder (GP) in cement-based materials was studied by using X-ray diffraction, thermo gravimetric and differential thermal analysis, and scanning electron microscopy techniques. The compressive strength was also tested. Test results indicate that high curing temperature is effective in promoting the pozzolanic reaction of GP, which contributes to improve the mechanical and microstructure performance. Besides, pozzolanic reaction is found around the unhydrated GP particle and formed C–S–H gel instead of ASR. This research can provide a new approach of improving the reaction activity of GP and lay a theoretical basis for the application of GP in precast concrete products, mass concrete or concrete construction during hot season.

Inhibitory Effect of Waste Glass Powder on ASR Expansion Induced by Waste Glass Aggregate

Detailed research is carried out to ascertain the inhibitory effect of waste glass powder (WGP) on alkali-silica reaction (ASR) expansion induced by waste glass aggregate in this paper. The alkali reactivity of waste glass aggregate is examined by two methods in accordance with the China Test Code SL352-2006. The potential of WGP to control the ASR expansion is determined in terms of mean diameter, specific surface area, content of WGP and curing temperature. Two mathematical models are developed to estimate the inhibitory efficiency of WGP. These studies show that there is ASR risk with an ASR expansion rate over 0.2% when the sand contains more than 30% glass aggregate. However, WGP can effectively control the ASR expansion and inhibit the expansion rate induced by the glass aggregate to be under 0.1%. The two mathematical models have good simulation results, which can be used to evaluate the inhibitory effect of WGP on ASR risk.

SEM Analysis of the Interfacial Transition Zone between Cement-Glass Powder Paste and Aggregate of Mortar under Microwave Curing

In order to investigate the effects of microwave curing on the microstructure of the interfacial transition zone of mortar prepared with a composite binder containing glass powder and to explain the mechanism of microwave curing on the improvement of compressive strength, in this study, the compressive strength of mortar under microwave curing was compared against mortar cured using (a) normal curing at 20 ± 1 °C with relative humidity (RH) > 90%; (b) steam curing at 40 °C for 10 h; and (c) steam curing at 80 °C for 4 h. The microstructure of the interfacial transition zone of mortar under the four curing regimes was analyzed by Scanning electron microscopy (SEM). The results showed that the improvement of the compressive strength of mortar under microwave curing can be attributed to the amelioration of the microstructure of the interfacial transition zone. The hydration degree of cement is accelerated by the thermal effect of microwave curing and Na+ partially dissolved from the fine glass powder to form more reticular calcium silicate hydrate, which connects the aggregate, calcium hydroxide, and non-hydrated cement and glass powder into a denser integral structure. In addition, a more stable triangular structure of calcium hydroxide contributes to the improvement of compressive strength.

Effect of various alkalis on hydration properties of alkali-activated slag cements

The effect of sodium silicate (NS system) and sodium hydroxide (NH system) on hydration properties of alkali-activated slag (AAS) cements is investigated, and more attention has been paid to the hydration kinetics in this paper. The increase of Na2O dosage tends to promote higher early strength of the cements, but lower strength gain at later, while increasing SiO2 dosage leads to improve both early and later strength. The hydration of the two AAS cements proceeds through three processes after induction period finished, namely nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D). With the increased Na2O dosage and decreased SiO2 dosage, the NG and I processes are shortened. The hydration rate during NG and I processes is also accelerated. CSH gel is the main hydrates of all AAS cements, but the activator type and content have impact on the minor hydration products.

Study on Strength and Microstructure of Cement-Based Materials Containing Combination Mineral Admixtures

The compressive strength of complex binders containing two or three blended mineral admixtures in terms of glass powder (GP), limestone powder (LP), and steel slag powder (SP) was determined by a battery solution type compressive testing machine. The morphology and microstructure characteristics of complex binder hydration products were also studied by microscopic analysis methods, such as XRD, TG-DTA, and SEM. The mechanical properties of the cement-based materials were analyzed to reveal the most appropriate mineral admixture type and content. The early sample strength development with GP was very slow, but it rapidly grew at later stages. The micro aggregate effect and pozzolanic reaction mutually occurred in the mineral admixture. In the early stage, the micro aggregate effect reduced paste porosity and the small particles connected with the cement hydration products to enhance its strength. In the later stage, the pozzolanic reaction of some components in the complex powder occurred and consumed part of the calcium hydroxide to form C-S-H gel, thus improving the hydration environment. Also, the produced C-S-H gel made the structure more compact, which improved the structure’s strength.

Study on Behavior of RPC Filled Steel Tubular Stub Columns Under Axial Compression

Reactive powder concrete (RPC) with compressive strength higher than 170 MPa was prepared by using ordinary Portland cement, silica fume, ground granulated blast-furnace slag or fly ash. RPC shows high strength, constant Poisson’s ratio, high compressive peak strain but post-peak brittle failure. Based on the RPC mechanical behavior study, investigation of the interaction between steel tubes and core RPC was performed, in view of its effect on the bearing capacity and deformability of RPC filled steel tubular (RPCFT) stub columns subjected to axial loading. RPCFT stub columns have very high ductility and alleviate the RPC disadvantage of brittle failure. However, the confinement effect of steel tubes on RPC is lower than that of normal strength concrete and thus, it can be neglected during the design process for convenience and safety.

Contrastive Numerical Investigations on Thermo-Structural Behaviors in Mass Concrete with Various Cements

This work is a contrastive investigation of numerical simulations to improve the comprehension of thermo-structural coupled phenomena of mass concrete structures during construction. The finite element (FE) analysis of thermo-structural behaviors is used to investigate the applicability of supersulfated cement (SSC) in mass concrete structures. A multi-scale framework based on a homogenization scheme is adopted in the parameter studies to describe the nonlinear concrete behaviors. Based on the experimental data of hydration heat evolution rate and quantity of SSC and fly ash Portland cement, the hydration properties of various cements are studied. Simulations are run on a concrete dam section with a conventional method and a chemo-thermo-mechanical coupled method. The results show that SSC is more suitable for mass concrete structures from the standpoint of temperature control and crack prevention.

Strength and microstructure of mortar containing glass powder and/or glass aggregate

The compressive strength of mortar containing glass powder (GP) and/or glass aggregate (GA) was tested, and its microstructure was also studied by thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), energy dispersive spectroscopic analysis (EDX), and X-ray diffraction (XRD) techniques. The incorporation of GA would decrease the compressive strength of the mortar in the absence of GP. Incorporating both GA and GP could change the hydration environment, promote pozzolanic reaction of GP and improve the compressive strength. GP does not lead to but can effectively control ASR (Alkali Silica Reaction). GP and GA do not transform the type of hydrates, but have a great influence on the amounts of hydration products, and generate more calcium silicate hydrate (C-S-H gel) with lower Ca/Si ratio. GP and GA with good gradation will make the microstructure denser.

Influence of Inertia and Low Active Mineral Admixture on Strength and Microstructure of Cement-Based Materials

Cement-based materials were investigated by comparing the strength and microstructure of pastes and mortar containing limestone powder or low quality fly ash. The compressive strength of the mortar at 28 and 90 d was examined whose microstructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis, and differential thermal analysis (TG-DTA). The results indicated that the strength of mortar decreased with increasing mineral admixtures. The limestone powder mainly acted as inert filler and hardly took part in the chemical reaction. Low quality fly ash may accelerate the formation of hydration products in samples with more chemically bonded water. This further resulted in a higher degree of cement hydration and denser microstructure, while the overall heat of hydration was reduced. At the early stage of hydration, low quality fly ash can be considered as an inert material whereas its reactivity at the later stage became high, especially for ground low quality fly ash.

Influence of Glass Powder on Hydration Kinetics of Composite Cementitious Materials

The influence of glass powder (GP) on hydration kinetics of composite cementitious materials has been investigated by isothermal calorimetry test and hydration kinetics methods in this paper. The hydration heat emission rate and hydration heat decrease gradually while the induction and acceleration period increase with the increase of GP content. According to Krstulovic-Dabic model, the hydration process of composite cementitious materials containing GP is controlled by a variety of complicated reaction mechanisms, which can be divided into three periods: nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D). The NG and I process are shortened after incorporating GP.