Xiao-Yong Wang

Simulation of Low-Calcium Fly Ash Blended Cement Hydration

In normal and high-strength concrete, low-calcium fly ash (FL) is a mineral admixture that has been widely used. Due to pozzolanic activity in a fly ash alumino-silicate glass phase, hydration is much more complex in cement blended with fly ash than in ordinary portland cement. A kinetic hydration model is presented in this paper which has its basis in a multi-component concept and through which cement-FL blend hydration can be simulated. Both portland cement hydration and pozzolanic activity are considered by the proposed model, which starts with a concrete mixture proportion. The following properties of hydrating cement-FL blends as a hydration time function are predicted in this paper by application of the proposed model: development of FL-concrete compressive strength, chemically bound water, porosity, heat evaluation, calcium hydroxide content, and reaction ratio of fly ash. For the results of the experiment performed in this study, good agreement is shown in the prediction results.

Analysis of the Optimum Usage of Slag for the Compressive Strength of Concrete

Ground granulated blast furnace slag is widely used as a mineral admixture to replace partial Portland cement in the concrete industry. As the amount of slag increases, the late-age compressive strength of concrete mixtures increases. However, after an optimum point, any further increase in slag does not improve the late-age compressive strength. This optimum replacement ratio of slag is a crucial factor for its efficient use in the concrete industry. This paper proposes a numerical procedure to analyze the optimum usage of slag for the compressive strength of concrete. This numerical procedure starts with a blended hydration model that simulates cement hydration, slag reaction, and interactions between cement hydration and slag reaction. The amount of calcium silicate hydrate (CSH) is calculated considering the contributions from cement hydration and slag reaction. Then, by using the CSH contents, the compressive strength of the slag-blended concrete is evaluated. Finally, based on the parameter analysis of the compressive strength development of concrete with different slag inclusions, the optimum usage of slag in concrete mixtures is determined to be approximately 40% of the total binder content. The proposed model is verified through experimental results of the compressive strength of slag-blended concrete with different water-to-binder ratios and different slag inclusions.

Analysis of Compressive Strength Development and Carbonation Depth of High-Volume Fly Ash Cement Pastes

High-volume fly ash (HVFA) concrete, which typically has 50 to 60% fly ash as the total cementitious material content, is widely used to achieve sustainable development in the concrete industry. Strength development and carbonation are critical research topics for using HVFA concrete. This paper presents a numerical procedure to evaluate the strength development and carbonation depth of HVFA concrete. This numerical procedure consists of a hydration model and a carbonation reaction model. The hydration model analyzes the fly ash dilution effect and the pozzolanic reaction. The amount of carbonatable materials, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), are calculated using reaction degrees of cement and fly ash. The compressive strength development of cement-fly ash blends are evaluated from CSH contents. The calculation results from the hydration model, such as the amount of carbonatable materials and the porosity, are used as input parameters for the carbonation reaction model. By considering the effects of material properties and environmental conditions, the carbonation reaction model analyzes the diffusivity of carbon dioxide and the carbonation depth of HVFA concrete with different curing conditions, different fly ash contents, and different water-binder (w/b) ratios.

Evaluation of the Chemical and Mechanical Properties of Hardening High-Calcium Fly Ash Blended Concrete

High-calcium fly ash (FH) is the combustion residue from electric power plants burning lignite or sub-bituminous coal. As a mineral admixture, FH can be used to produce high-strength concrete and high-performance concrete. The development of chemical and mechanical properties is a crucial factor for appropriately using FH in the concrete industry. To achieve sustainable development in the concrete industry, this paper presents a theoretical model to systematically evaluate the property developments of FH blended concrete. The proposed model analyzes the cement hydration, the reaction of free CaO in FH, and the reaction of phases in FH other than free CaO. The mutual interactions among cement hydration, the reaction of free CaO in FH, and the reaction of other phases in FH are also considered through the calcium hydroxide contents and the capillary water contents. Using the hydration degree of cement, the reaction degree of free CaO in FH, and the reaction degree of other phases in FH, the proposed model evaluates the calcium hydroxide contents, the reaction degree of FH, chemically bound water, porosity, and the compressive strength of hardening concrete with different water to binder ratios and FH replacement ratios. The evaluated results are compared to experimental results, and good consistencies are found.

Evaluation of Properties of Concrete Incorporating Fly Ash or Slag Using a Hydration Model

Granulated slag from metal industries and fly ash from the combustion of coal are industrial by-products that have been used widely as mineral admixtures in normal and high-strength concrete. Because of the reaction between calcium hydroxide and fly ash or slag, the hydration of concrete containing fly ash or slag is much more complex than that of portland cement. In this paper, the production of calcium hydroxide in cement hydration and its consumption in the reaction of mineral admixtures is considered to develop a numerical model that simulates the hydration of concrete containing fly ash or slag. The properties of concrete incorporating fly ash or slag, such as the adiabatic temperature increase, chemically bound water, reaction degree of mineral admixture, and the compressive strength, are determined by the contribution of both cement hydration and the reaction of the mineral admixtures. The proposed model is verified with experimental data from concrete with different water to cement ratios and mine...

Prediction of Time-Dependent Chloride Diffusion Coefficients for Slag-Blended Concrete

The chloride diffusion coefficient is considered to be a key factor for evaluating the service life of ground-granulated blast-furnace slag (GGBS) blended concrete. The chloride diffusion coefficient relates to both the concrete mixing proportions and curing ages. Due to the continuous hydration of the binders, the capillary porosity of the concrete decreases and the chloride diffusion coefficient also decreases over time. To date, the dependence of chloride diffusivity on the binder hydration and curing ages of slag-blended concrete has not been considered in detail. To fill this gap, this study presents a numerical procedure to predict time-dependent chloride diffusion coefficients for slag-blended concrete. First, by using a blended cement hydration model, the degree of the binder reaction for hardening concrete can be calculated. The effects of the water to binder ratios and slag replacement ratios on the degree of the binder reaction are considered. Second, by using the degree of the binder reaction, the capillary porosity of the binder paste at different curing ages can be determined. Third, by using the capillary porosity and aggregate volume, the chloride diffusion coefficients of concrete can be calculated. The proposed numerical procedure has been verified using the experimental results of concrete with different water to binder ratios, slag replacement ratios, and curing ages.

Hydration and Durability of Concrete Containing Supplementary Cementitious Materials

Fly ash, slag, silica fume, and other supplementary cementitious materials (SCMs) are used more and more for producing modern concrete. SCMs can provide various benefits to the concrete industry, such as improving the workability, early-age performance, and durability of concrete structures, lowering the materials’ cost of proportions of concrete mix, and reducing greenhouse gas emissions.Thematerial performance of concrete containing SCMs is an important research theme for the sustainable development of the concrete industry. To meet the increasing requirements about knowledge of SCMs from concrete researchers and construction companies, in 2016, we proposed this special issue. This special issue aroused the interest of researchers around the world. 26 articles were finally published after careful reviews. The acceptance rate is about 45%. These articles cover different aspects of materials performance of SCMs blended concrete, such as chemical admixtures, hydration, strength development, shrinkage, chloride ingress, frost, corrosion, and service life evaluation.The integratedmaterial-structure studies, such as the influence of load on durability and structure performance under low temperature, are also presented. In addition, the analysis of durability-induced damage and repairing of damaged concrete structures are discussed in detail. In summary, this special issue covers material scale and structure scale and considers the production stage, service stage, and repair stage of structures. The detailed experimental studies, theoretical analyses, andwide and deep discussions will contribute to the realization, utilization, and development of SCMs. Finally, we are grateful to the authors, reviewers, and editors of this journal. The publication of this special issue embodies the efforts of those authors, reviewers, and editors.

Self Healing System for Concrete Surface Crack using Polymer based Coating Agent Incorporating Microencapsulated Healing Agent

In this paper, microencapsulated healing agent was embedded in the polymer matrix to obtain self healing properties. Microencapsulation of methacrylate using polyurea-formaldehyde as a shell material and studied the effect of agitation rate on capsule characteristics such as size, shell thickness, and surface morphology. The formation of microcapsules was confirmed by FTIR and TGA, and capsule characteristics were studied by optical microscopy and SEM. The self-healing effect was evaluated using permeability measurements and further confirmed by surface analytical tools including optical microscope. According to the experimental results, the microencapsulated healing system has the self-heaing ability for artificial cracks.

The Evaluation of Carbonation Depth of Concrete Incorporating Industrial By-Product Materials

Fly ash from the combustion of coal and silica fume from certain metallurgical operations, are among the industrial by-products that are widely used as mineral admixtures in Portland cement concrete to improve durability and produce high strength and high performance concrete. In addition, due to energy-saving and resource-conservation, both ecological and economical benefit can be achieved by using blended Portland cement. Due to the pozzolanic reaction between calcium hydroxide and fly ash or silica fume, compared with ordinary Portland cement, the carbonation of blended concrete is much more complex. In this paper, based on multi-component concept, a numerical model is built which can predict the carbonation of concrete containing fly ash or silica fume. The proposed model starts with a mix proportion of concrete and considers both Portland cement hydration reaction and pozzolanic reaction. The amount of hydration products which are susceptible to carbonate, such as calcium hydroxide (CH) and calcium s...