Portland cement has a limited shelf life because of the prehydration that can occur during storage. One approach to mitigating strength losses observed for concrete is to pretreat cement with a ...protective coating to slow the advance of prehydration. This study compared cement pretreatments with alkyl ketene dimer (AKD) wax and a combination of AKD + paraffin wax to a more traditional pretreatment approach using oleic acid. After exposing the treated cements to elevated temperature and humidity conditions, paste and mortar calorimetry tests showed improved resistance to prehydration reactions. The cements aged up to 12 weeks under the accelerated regime showed strength improvement for the mortars made with AKD and AKD + paraffin-treated cements relative to the mortars made with oleic acid-treated cement and mortars made with untreated cement. The wax can be added during clinker milling and additionally functions as a grinding aid.
In this study, several tests for supplementary cementitious materials (SCMs) were evaluated to find the best methods to rapidly screen out inert materials, measure overall reactivity, and ...differentiate between pozzolanicity and latent hydraulicity. The R3 matrix and lime reactivity tests were found to be the most effective at quickly screening out inert materials. However, slow-reacting materials may appear to have low reactivity in both tests and extending the test duration better depicts material reactivity. Additionally, SCMs with higher alumina content perform better in the R3 tests due to the higher heat release and more bound water associated with the formation of calcium aluminate hydrates compared to calcium silicate hydrates, creating reactivity bias when compared to SCMs with lower alumina content. Measuring the calcium hydroxide content of R3 pastes, through thermogravimetric analysis or single point mass loss, can also differentiate between pozzolanic and hydraulic materials.
•Early hydration properties and kinetics of multi-composite cement was evaluated.•The Krstulovic–Dabic model described three gap-graded groups segmentally.•Cumulative heat simulated by the Knudsen ...equation close to test results.
To simulate the hydration process of multi-composite cement pastes with supplementary cementitious materials (SCMs), this paper investigates the early hydration performance, and reaction kinetics of compound system. Significantly, the exothermic characteristics of binary, ternary and quaternary cement blends with three typical SCMs were experimentally evaluated through isothermal calorimetric test, and the hydration mechanism and kinetics parameters were calculated and analysed quantitatively. A second exothermic peak was observed in the cement blends in various particle size groups, and the hydration heat peak varied amongst different complex conditions. The Krstulovic–Dabic model segmentally described the relationship between the rate and degree of hydration of the fine-grained, coarse-grained, and normal-grained groups. The cumulative heat release simulated by the Knudsen equation was within 10% of the experimental results of 72 h isothermal calorimetric measurements. Hence, isothermal calorimetric, combined with kinetic models, is a valuable method for investigating the hydration kinetics of multi-composite cement blends.
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•Hydraulic and pozzolanic behavior of basic oxygen furnace slag (BOFS), ladle furnace slag (LFS), and ground granulated blast furnace slag (GGBFS) are studied.•Multiple tests are performed to ...determine the feasibility of these slags as SCMs.•GGBFS shows the best performance; BOFS and LFS should not be used as SCMs as-is.•The combined use of test methods is more accurate.
Limited applications for the large amounts of steel slags produced globally exist. In this study, the hydraulic and pozzolanic behavior of basic oxygen furnace slag (BOFS) and ladle furnace slag (LFS) are studied and contrasted with the behavior of ground granulated blast furnace slag (GGBFS). Pozzolanic test, isothermal calorimetry, thermogravimetric analysis, and compressive strength test are performed to determine the feasibility of these slags as supplementary cementitious materials (SCMs). The pozzolanic test is performed by measuring the heat release and calcium hydroxide consumption of slag-calcium hydroxide blends at 50 °C and pH 13.5. The other tests are performed on cementitious pastes with 20% slag replacement by mass at 23 °C and 50 °C. GGBFS shows the best performance among all slags in the tests, followed by BOFS, followed by LFS. It is suggested that BOFS and LFS should not be used as SCMs as-is. The poor performance of LFS is due to flash setting, likely caused due to the rapid reaction of C12A7, which causes hydration retardation and poor strength gain. The BOFS shows moderate performance as it has low hydraulic activity, likely explained by its low amorphous content and the presence of low amount of reactive crystalline phases. An important finding from this study is that in order to state whether materials could be used as SCMs or not, the combined use of pozzolanic test, isothermal calorimetry, and compressive strength test is more accurate than the use of only one test method. While the results obtained may here not be broadly generalizable to other materials due to variations in slag chemistry, the approach suggested may be generalizable to obtain insights into whether any powder may be used as SCM.
Research has shown that reaction kinetics and physical transformation during alkali-activation of aluminosilicate materials are sensitive to both the compositions of raw precursors and the alkaline ...solution. Methods that allow for early observations relating to reaction kinetics, and that capture early-age physicochemical transformations with sufficient accuracy, can assist design engineers in bringing this new generation of binders to market. In this study, reaction heat and ultrasonic pulse velocity (UPV) evolutions of low calcium fly ash activated with alkaline solutions of different concentrations, and substituted with various dosages of ground granulated blast furnace slag (GGBFS), were systematically monitored using isothermal calorimetric and portable ultrasonic testing facilities. The incorporation of slag in a fly ash-based system influences the reaction kinetics, rate of physical transformation and morphological features. The study shows that UPV can capture the effect of slag addition on the microstructure densification, which is confirmed by measurements of heat evolution and SEM-EDS microstructural observations. A linear correlation of UPV was identified with the heat evolved. It was further shown that UPV tests can successfully capture workable time of alkali-activated fly ash paste blends that contain at least 10% of slag, noting that mixtures without any slag did not set within the first 24 h of activation. Further, improved dissolution of species, leading to an increased heat evolution, was observed with increasing activator alkalinity. SEM-EDS microstructural characterisation reveals an advanced dissolution of particles in a more alkaline environment, while higher silicate content leads to a more homogeneous morphology. The findings of this research will assist in the utilisation of alkali-activated materials in construction practice.
•Effects of GGBFS, FA and SF to the hydration behavior of calcium aluminate cement at 20 °C and 38 °C are studied.•The rate of hydration was higher and earlier at 38 °C than at 20 °C.•An increase in ...mineral admixture content contributed to higher capillary water absorption.•The increase in temperature caused lower capillary water absorption.•10% addition of GGBFS and FA can be accepted as the optimum solution among all the productions in this study.
Cement-based materials that are produced with calcium aluminate cement (CAC) exhibit severe strength losses with time and temperature due to the conversion of metastable hydrates (CAH10 and C2AH8) into the stable hydrates (C3AH6 and AH3). On the other hand, using mineral admixtures at different ratios during the production of cement-based materials change the hydration behavior and, thus, mechanical properties of these materials. Therefore, this research focuses on the effects of mineral admixtures on the properties of CAC mortars at two different curing temperatures (20 °C and 38 °C). Mortars were prepared by using constant CAC content, and the sand was replaced by class F fly ash (FA) as 10%, 30%, 60%, granulated ground blast furnace slag (GGBFS) as 10%, 30%, 60% and silica fume (SF) as 5%, 10%, 15%. In addition to fresh mortar tests, other tests, including isothermal calorimetry tests up to 72 h, the flexural and compressive strength tests at 3, 7, 28, and 90 days and the capillary absorption tests, were also conducted. The mineral admixtures, when used as sand replacement materials, accelerated the hydration reactions of CAC mortars. 10% replacement of sand by FA and especially GGBFS resulted in better mechanical strengths at 20 °C (7% and 16% increases in compressive strengths for 10% FA and 10% GGBFS replacements at 90 days). In addition, they were least affected with the increase in temperature to 38 °C as compared to other GGBFS and FA used mixes. On the other hand, silica fume used mixtures had relatively lower strengths, but they showed some improvements with the increase in temperature at later ages (10% and 25% increases at 90 days for 5% and 15% SF, respectively). GGBFS and FA additions in different amounts decreased the heat of hydration values at 38 °C as compared to 20 °C (except 10% GGBFS addition) while silica fume increased the values.
•A 1-m concrete cube was developed to obtain ATR using cube’s center temperature.•Required cube insulation was provided for ambient conditions between −10 °C to 30 °C.•Heat of hydration measurements ...were demonstrated during four on-site castings in WV.•Hydration heat from concrete containing slag or fly ash replacement was obtained.•ATRs from on-site cube compared well with adiabatic and isothermal calorimetry data.•Heat generation functions were accurately obtained using the ATRs measured on-site.
In this study, measurements of the heat of hydration of mass concrete delivered on-site were proposed. A one-meter concrete cube, cast adjacent to the real structure, was developed as an on-site semi-adiabatic calorimeter. A table was established for the required insulation of the cube in different ambient temperatures. To simplify the measurement process and cost, a method was developed to obtain the concrete adiabatic temperature rise (ATR) by simply using the measured temperature at the center of the cube. The finite element method (FEM) was used to calculate the required insulation for various ambient conditions between −10 to 30 °C so that the ATR could be accurately estimated using only the measured center temperature. The predicted ATR and the actual ATR showed less than 1% error. The proposed heat of hydration measurement was tested during four on-site field castings at three different districts in West Virginia. Two of the field batches contained 50% Grade 100 ground granulated blast furnace slag replacements. The fourth field batch had 30% Class F fly ash replacement. The material collected from each field test was also used to perform laboratory adiabatic and isothermal heat of hydration measurements. The ATR calculated from the on-site cube data compared well with the results from both adiabatic and isothermal calorimetry tests. The heat of hydration parameters were successfully obtained based on the ATR calculated from each on-site casting. Results show that the proposed on-site heat measurement can be a simple and accurate approach to measure the heat of hydration of a delivered concrete batch.
Because ready-mixed concrete is placed under a wide variety of environmental conditions, the influence of temperature on the hydration reactions and the accompanying setting process is of critical ...importance. While contractors are generally quite comfortable with the temperature sensitivity of conventional ordinary Portland cement (OPC) concretes, more sustainable mixtures containing high volumes of fly ash (HVFA), for example, often present problems with delayed setting times and increased temperature sensitivity. Based on isothermal calorimetry and Vicat needle penetration measurements, this study demonstrates that the high temperature sensitivity of such HVFA mixtures can be effectively moderated by the replacement of a portion of the fly ash with a fine calcium carbonate powder. In addition to accelerating and amplifying hydration and reducing setting times at a given temperature, the presence of the fine CaCO3 powder also lowers the apparent activation energy for setting for temperatures below25°C. The reactivity of the CaCO3 in these mixtures is quantified using thermogravimetric analysis. Comparison of results for CaCO3 powders of nominal sizes of 1μm and 17μm, replacing 10% by volume of the cement in an OPC mixture, indicates that the former is highly superior in accelerating/amplifying hydration and reducing setting times.
•The hydration kinetics of MOS with citric acid was evaluated via isothermal calorimetry.•The hydration kinetics of MOS cement was modeled with a scale factor model.•The individual reaction order in ...CA and apparent activation energy was obtained.
The hydration kinetics of magnesium oxysulfate cement (MOS) with and without citric acid (CA) was evaluated via isothermal calorimetry. A series of tests were conducted with different MgSO4 solution-to-MgO ratios (r) and MgO with different activities at 15 °C and 25 °C. The test results indicated that the effect of CA on the overall cement hydration rate was determined by the CA dose (w) primarily and can be simulated by a generalized scale factor model. The heat flow and cumulative heat evolution of slurries with different CA dosages could be accurately predicted using the scale factor (f) model. There was a linear relationship between lgf and lg(w/w0), so the individual reaction order in CA could be obtained. The effect of temperature on the hydration kinetics of MOS cement with and without CA was modeled with the original scale factor model developed from the Arrhenius equation, and the apparent activation energy obtained was 66.3 and 74.9 kJ/mol, respectively. This study provided a basis for further in-depth research of the kinetic mechanism of the MOS hydration reaction.
