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Conventionally, isothermal calorimetry and ASTM C186 heat of hydration results are reported on a per mass of cement (powder) basis, with typical units being J/g (cement) for example. Based on the recognition that it is the filling of porosity with hydration products that is chiefly responsible for strength development in cement-based materials, there may be merit in instead reporting these results on a per unit volume of (initial) water basis. This paper examines a database of well over 200 mortar mixtures to investigate the relationship between heat release and mortar cube compressive strength development. For reasonably low water-to-cementitious materials ratios (w/cm < 0.43), a single universal straight line relationship with some scatter is obtained. Based on numerous experimental data sets and accompanying theoretical computations, the effects of w/cm, sand volume fraction, cement chemical composition, sulfate content, cement fineness, the incorporation of a high range water reducing admixture, and curing conditions on this universal relationship are all considered. Fifty data points from the Cement and Concrete Reference Laboratory (CCRL) proficiency sample program are analyzed to develop a linear relationship between ASTM C109 mortar cube compressive strengths and ASTM C186 heats of hydration at 7 d and 28 d. The application of this relationship for virtual testing is also evaluated. In this case, computer simulations would be employed to predict the heat of hydration vs. time for a particular cement and the developed equations would be employed to convert this heat release to a strength prediction at the age(s) of interest. In general, it appears that these relationships can be used to predict mortar cube compressive strengths based on measured heats of hydration, within about ± 10 % of the experimentally measured strengths. A preliminary analysis of a single dataset for concretes with and without limestone replacement for cement indicates that the linear relationship between strength and heat release likely holds for concretes as well as mortars.
Deterioration has been observed at the joints of many portland cement–based concrete pavements in midwestern U.S. states. It has been shown that this damage can be caused by either classic freeze–thaw behavior triggered by high saturation levels or a chemical reaction that occurs between the deicing salt (in this study, calcium chloride) and the cementitious matrix. The objective of this study was to show that low-temperature differential scanning calorimetry could be used to quantify the potential for the chemical reaction between the salt and matrix (i.e., calcium oxychloride formation). The formation of calcium oxychloride is expansive and may lead to significant cracking and spalling without exposure to freeze–thaw cycles. This study examined pastes made with ordinary portland cement; portland limestone cement; and portland cement combined with fly ash, slag, or silica fume. The results indicate that the amount of calcium oxychloride formation that occurs is not significantly different between ordinary portland cements and portland limestone cements. The addition of supplementary cementitious materials reduces the formation of the calcium oxychloride, presumably because of the reduction of calcium hydroxide from dilution, the pozzolanic reaction, and a reduction in the alkali content in the pore solution. The results also indicate that sealers can be used to create a barrier between the salt and the calcium hydroxide or that they can react with the calcium hydroxide, thereby reducing the amount of calcium oxychloride.
High volume fly ash (HVFA) concretes have been used in the past; however HVFA has been primarily advocated for use in mass construction applications. Recent interest in developing more sustainable construction materials has led to an increased interest in utilizing these HVFA mixtures in transportation structures such as pavements and bridges. These mixtures have a reduced carbon footprint, in addition to other improvements in the material performance. This paper presents a study utilizing the dual ring test to assess the benefits of the HVFA mortar mixtures with respect to reducing early age cracking. Three mortar mixtures were prepared with a water-to-cement ratio of 0.30. The first mixture is a plain cement mortar, the second mixture is a mortar where 40 % of the cement (by volume) was replaced with C class fly ash, and the third mixture is a mortar where 40 % of the cement (by volume) was replaced with C class fly ash and prewetted lightweight aggregate (LWA) to provide internal curing (IC). The cracking potential due to thermal and autogenous shrinkage was assessed. Results show a lower risk of shrinkage cracking in the HVFA mixture with internal curing. The IC mixture made using HVFA is more robust for construction at early ages.
Internally cured (IC) concrete is frequently produced in North America using pre-wetted lightweight aggregate (LWA). One important aspect associated with the production of quality IC concrete is the accurate determination of the moisture content, including absorbed moisture and surface moisture of the LWA. Knowledge of the moisture content enables aggregate moisture corrections to be made for the concrete mixture, thereby enabling an accurate water-to-cement ratio to be maintained. Two methods for determining the moisture content of LWA include the specified ASTM C1761-13b "paper towel method" and a method that uses a centrifuge (Miller, Barrett, Zander, & Weiss, 2014). There are limited data available on the variability associated with either of these approaches when the test is performed by multiple users. In this study, the absorption of four commercially available LWAs was tested by a single operator in a single laboratory using the centrifuge method. In addition, the absorption of three commercially available LWAs was tested by 25 users performing both experimental methods. This article provides an estimation of precision associated with both a single operator and multiple operators performing both the paper towel method and the centrifuge method to find the absorption of pre-wetted lightweight fine aggregate.
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