Influence of Bottom Ashes with Different Water Retainabilities on Properties of Expansive Mortars and Expansive Concretes

This study investigates the influence of bottom ashes with different water retainabilities as an internal curing material on the performances of mixtures containing an expansive additive and fly ash. Two series of experiments were conducted: mortar containing expansive agent (expansive mortar) with a controlled w/b ratio and concrete containing expansive agent (expansive concrete) with a controlled initial slump. Test results indicate that workability of expansive mortar is improved due to retained water of bottom ash. Compressive strength of expansive mortar with bottom ash decreases. Total shrinkage of the expansive mortars, with a constant w/b, increases with the use of bottom ashes that have high water retainability in the condition of 7 days of water curing and then air curing. However, by using bottom ashes, compressive strength increases when the slump of the expansive concrete is controlled due to decrease of w/b ratio. The internal curing ability of bottom ashes leads to enhanced expansion of expansive mortars with sealed curing and expansive concretes with moist curing, reducing total shrinkage of expansive mortars with air curing. It was found by DTG analysis that expansive concretes with higher expansion containing bottom ash with higher water retainability had a higher amount of ettringite

Self-healing Behavior of Expansive Mortars with Fly Ash and Bottom Ash

In this paper, the effectiveness of fly ash (FA) and bottom ash (BA) on the self-healing (S-H) behavior of expansive concrete was experimentally investigated by using the crack closing ratio and water flow rate as indicators of the self-healing ability. To heal cracks that may be caused by shrinkage, high CaO-SO3-free lime fly ash (FAB), high CaO fly ash (FAA), and low CaO fly ash (FAR), and one type of expansive additive were used as the partial binder replacement materials. A pre-soaked bottom ash with high water retainability was used as a water-providing agent for the internal curing (IC) technique, to reduce shrinkage and enhance long-term hydration. Pre-cracked mortar samples were prepared in a disc shape with a fixed crack width of 0.1 mm. After crack creation, the crack width ratio and water flow rate were monitored every 7 days for 3 months. It was observed that expansive mortars with 30% fly ash showed significant improvement in the self-healing ability when compared to the non-fly ash mortar.   The use of 10% bottom ash showed enhanced self-healing ability in expansive mortar. Moreover, using both fly ash and bottom ash showed significant improvement in the self-healing behavior

Compressive Strength, Free Expansion and Shrinkage of Expansive Concrete containing Fly Ash

This study is aimed to investigate effect of fly ash on compressive strength, free expansion and shrinkage of expansive concrete. High CaO and low CaO fly ashes are used in this study. The replacement percentages of total binders by fly ash are 0 and 30% by weight. The replacements of expansive additive are 0, 20 and 30 kg/m3 of concrete. The test results revealed that the use of fly ash especially the high CaO fly ash can enhance expansion of expansive concrete at early age. The use of fly ash also reduces shrinkage at long term of the expansive concrete when compared with that of the expansive concrete without fly ash. Therefore, dosage of expansive additive in concrete can be reduced when fly ash is incorporated in the expansive concrete. An enhanced expansion of the expansive concrete is mainly due to a formation of ettringite which is verified by XRD/Rietveld analysis. The compressive strength is tested in conditions of unconfinement and confinement. The results revealed that the compressive strength of expansive concrete treated under confined condition is improved. The expansive concrete containing fly ash with a superior expansion is more effective to improve the confined compressive strength. This is because the restricted expansion under confinement leads to an improvement of microstructure, so making denser paste structure and gaining more strength

Deterioration in Sulfuric Acid of Cement Pastes incorporating High CaO and Low CaO Fly Ashes

This research studies the deterioration in sulfuric acid solution (pH 1) of cement pastes with fly ash. Effects of three major factors affecting the acid attack behavior are described. First, for the water to binder ratio, it was found that cement pastes with a higher water to binder ratio (w/b of 0.40) have a lower mass loss in sulfuric acid solution than those with a lower water to binder ratio (w/b of 0.25). In addition to the known mechanism of higher porosity in higher w/b pastes which makes the higher w/b pastes to be able to accommodate more gypsum, another mechanism was described based on the different abilities of calcium ion and sulfate ion to diffuse out of and into the pastes, respectively. Second, the type and content of binder provide a great influence on the degradation of cement pastes. The test of cement pastes with 30% and 50% fly ash replacement demonstrated that the fly ashes decrease the deterioration of pastes in sulfuric acid solution. In addition, it was observed that fly ash with low calcium oxide provided better resistance to sulfuric acid attack than fly ash with high calcium oxide did. Finally, the characteristics of the deterioration of paste specimens due to sulfuric acid attack was found to correlate well with CaO/SiO2 ratio

Degree of Hydration and Mass Balance Equations for Determination of Mix Proportion of Hardened OPC Concrete

A method for estimating mix proportion of hardened OPC concrete is proposed in this study. A set of mass balance equations was formed to calculate content of concrete compositions including cement, water, sand, and coarse aggregate. The degree of hydration of cement was taken into account in the analysis in order to cover the effect of age of concrete. In order to verify the accuracy of the proposed method, the determination of mix proportion of concrete was conducted on concrete specimens prepared in the laboratory with known mix proportions. Moreover, the mix proportion of concrete at different ages were calculated both with and without consideration of time-dependent degree of hydration in the analysis to clarify the enhanced capability of the proposed method when the effect of age of concrete is considered. It was found from the analytical results that the proposed method could be used to estimate mix proportion of concrete, with a satisfactory precision, at any age. The calculation of mix proportion of hardened concrete with consideration of time-dependent degree of hydration provided less error than that without consideration of the degree of hydration. The percentage of error of the mix proportion prediction of the concrete samples was less than 5%

Models for Predicting Free Water and Specific Heat of Pastes Containing Ground Granulated Blast Furnace Slag

Abstract: This paper aims to investigate early age behavior in terms of free water content and specific heat for hardening cement paste incorporating Ground Granulated Blast Furnace Slag. Experiments were conducted to obtain free water and specific heat of slag-cement pastes by varying water to binder ratios and slag replacement levels. Free water to total binder ratios for pastes with w/b of 0.40 and slag replacements of 45% and 75% are 0.23 and 0.25 at 3 days and 0.17 and 0.19 at 28 days, respectively. Specific heat values for similar mixtures are 0.26 and 0.30 at 3 days and 0.23 and 0.25 at 28 days. Results showed that specific heat decreases as the amount of free water decreases. The slag substitution resulted in high specific heat and free water at early age but tends to decrease in long term due to enhanced reaction kinetics. Models were proposed to compute free water and specific heat by modifying existing models. The model simulations can be used to predict the measured values accurately

Effects of Sand Powder on Sulfuric Acid Resistance, Compressive Strength, Cost Benefits, and CO2 Reduction of High CaO Fly Ash Concrete

This article studies the efficiency of sand powder as a supplementary cementitious material (SCM) in improving the sulfuric acid resistance of concrete incorporated with high CaO fly ash. Besides, the effects of sand powder on compressive strength development, mitigation of carbon dioxide emission, and cost-effectiveness are addressed. Paste mixtures with W/B ratios of 0.25 and 0.40 were used in this study for the performances of sulfuric acid resistance and long-term compressive strength development. The test results indicated that sand powder could reduce the weight loss of the tested paste specimens in sulfuric acid solution with a pH of 1, compared to the control specimens, especially for the specimens incorporated with high CaO fly ash. The sand powder addition could also increase the compressive strength of cement pastes at the age of 90 days by 26.27% and 43.80% for W/B ratios of 0.25 and 0.40, respectively. The use of sand powder in the evaluated concrete mixture could also reduce CO2 emission by 23.23% and lower the cost of the mixtures by 8.05%, compared to the control mixture. The addition of sand powder could significantly increase the sulfuric acid resistance, compressive strength, and economic benefits and reduce the CO2 emission of high CaO fly ash-cement-based materials

Models for Predicting Hydration Degree and Adiabatic Temperature Rise of Mass Concrete containing Ground Granulated Blast Furnace Slag

Predicting adiabatic temperature rise is essentially useful for investigating thermal cracking potential especially in early stage of mass concrete.  Existing prediction methods and models have some problems such as constant thermal properties are mostly utilized for predicting temperature rise. This study is aimed to develop time-dependent models for predicting hydration degrees of cement and slag, free water amount, specific heat, and total heat generation of concrete incorporating slag.  These models are then composed to predict the adiabatic temperature rise of mass concrete incorporating slag.  The model is able to predict adiabatic temperature rise in mass concrete with different water to binder ratios, slag replacements, physical properties of slag, and initial temperature conditions.  The validity of the proposed model was evaluated by comparing the model predictions with test results for adiabatic temperature rise of slag concrete.  The model simulations can be used to predict the experimentally measured data from differentPredicting adiabatic temperature rise is essentially useful for investigating thermal cracking potential especially in early stage of mass concrete.  Existing prediction methods and models have some problems such as constant thermal properties are mostly utilized for predicting temperature rise. This study is aimed to develop time-dependent models for predicting hydration degrees of cement and slag, free water amount, specific heat, and total heat generation of concrete incorporating slag.  These models are then composed to predict the adiabatic temperature rise of mass concrete incorporating slag.  The model is able to predict adiabatic temperature rise in mass concrete with different water to binder ratios, slag replacements, physical properties of slag, and initial temperature conditions.  The validity of the proposed model was evaluated by comparing the model predictions with test results for adiabatic temperature rise of slag concrete.  The model simulations can be used to predict the experimentally measured data from differen