Hydration, Setting and Crack-Resistance Properties of Activated HVFACs at Early Stages
نویسندگان
چکیده
In order to develop a simple and effective activation method of low calcium fly ash concrete (FAC) and to understand their basic properties, the present paper experimentally investigates the influences of the volume of fly ash (FA), the dosage of the activator (AC) and the water to binder ratio (w/b) on the hydration, setting times and the crack-resistance properties of activated FACs. Results verify that increasing FA can effectively reduce the hydration heat of the FA-cement system and increase the setting time of FACs, as well as indicate that FA can delay the occurrence of the initial crack and reduce the maximum width and total area of cracks in these concretes through a new quantitative test. The curing time of concrete affects the hydration heat of FA paste with/without AC. When the curing time of FAC increases, the decrease in amplitude of hydration heat reduces gradually. Additionally, it was found that the used ACs can effectively stimulate the activity of FA in Portland cement (PC) systems, which reduces their setting time slightly. However, high dosages of ACs also accelerate the development of early cracks in the FACs, as well. According to the study, the combined activator (10% CaO + 1.5% Na2SO4) was suggested as the most effective way to promote FA-PC concrete for obtaining acceptable properties at early stages. Besides, the existing calculation model for predicting the setting times of FACs was examined and modified to be more suitable to FACs activated by 10% CaO + 1.5% Na2SO4. The proposed model was verified and can evaluate the experimental results well.
منابع مشابه
The Hydration Products of a Refractory Calcium Aluminate Cement at Low Temperatures
Calcium aluminates (CA) are the most important hydraulically setting cements used for preparing refractory castables, because they develop high strength at very early ages after placements. The anhydrous phases of this kind of cements are CA, CA2 and traces of C12A7 and alpha-alumina. The major hydraulic phase in all of the CA cements including ciment fondu...
متن کاملIMPROVING HYDRATION RESISTANCE OF MAGNESIA-DOLOMA REFRACTORIES BYIRON OXIDE ADDITION
Abstract: There have been lots of studies to control the poor hydration resistance of dolomite refractories one of themost effective solutions has been the addition of magnesia to doloma. Using a co-clinker of magnesia-doloma as astarting material would provide more homogeneity in the properties of the product and has been published recently.On the other hand, addition of iron oxide to doloma h...
متن کاملCrack blunting, crack bridging and resistance-curve fracture mechanics in dentin: effect of hydration.
Few studies have focused on a description of the fracture toughness properties of dentin in terms of resistance-curve (R-curve) behavior, i.e., fracture resistance increasing with crack extension, particularly in light of the relevant toughening mechanisms involved. Accordingly, in the present study, fracture mechanics based experiments were conducted on elephant dentin in order to determine su...
متن کاملApplication of SCB Test and Surface Free Energy Method in Evaluating Crack Resistance of SBS Modified Asphalt Mixes
Cohesion properties of the binder matrix within asphalt mixes and adhesion characteristics of the asphalt binder and aggregate particles are the two major mechanisms resisting against cracking in asphalt mixes. This study is focused on estimating crack resistance of asphalt mixes at intermediate temperatures through evaluation of cohesion and adhesion properties of binder-aggregate systems usin...
متن کاملInvestigation of the effect of phosphate agent type on setting time, flowability, hydration and dehydration of magnesium phosphate cement.
Magnesium phosphate cements (MPC) are the most developed kind of chemically bonded ceramics which form through the reaction of magnesium oxide and soluble phosphate salts. Therefore, study of different magnesium phosphate cement systems is considered important according to the type of phosphate agent used. In this study, effect of mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP), and ...
متن کامل