Studies on effects of activators on properties and mechanism of hydration of sulphoaluminate cement

Liu

2021

Materials

Compared to ordinary Portland cement (OPC), calcium sulfoaluminate cement (CSA) displays very early-age strength and faster heat-releasing rate during hydration. In the present paper, the early hydration heat of CSA paste with influences of supplementary cementitious materials (SCMs) and water to cement (or binder) ratio (w/c) is systematically studied by measuring the heat-releasing rate using a calorimeter. Three traditional SCMs—silica fume (SF), fly ash (FA) and ground granulated blast furnace slag (SL)—were used in the study. A water to cement or binder ratio (w/c) between 0.19 and 0.73 was used in the mixtures. The results show that three exothermic peaks were presented during hydration—dissolution exothermic peak and two reaction exothermic peaks. With the w/c of 0.3, the first and second reaction peaks of the CSA paste are as high as 17.8 times and 4.1 times that of OPC paste, and the occurring time is much earlier than that of the OPC paste. The second reaction peak appears earlier, and the third reaction peak appears later in the pastes with addition of SF than in those without SF. Decreasing w/c can greatly reduce the two reaction peaks of the paste, and it looks that there is a critical value of w/c between 0.24 and 0.30. Above the critical value, the effect of w/c is minor, and below that the influence is obvious. An optimal use of SCMs in CSA pastes under different w/c can greatly decrease the heat releasing while maintaining the required strength.

Section: Introductionmentioning

confidence: 99%

Early Hydration Heat of Calcium Sulfoaluminate Cement with Influences of Supplementary Cementitious Materials and Water to Binder Ratio

Liu

2021

Materials

“…In addition, CSA cement with calcium sulfoaluminate as the main mineral has low CO 2 emission and low firing temperature during production compared to Portland cement (Winnefeld and Lothenbach 2010). Therefore, CSA cement may be selected as one of the most promising low CO 2 alternatives to OPC in view of sustainable development for modern concrete (Fu et al 2003;Gartner 2004;Glasser and Zhang 2001;Péra and Ambroise 2004;Quillin 2001). However, CSA cement sets rapidly, so the CSA cement concrete is currently used only for relatively small-scale repairs.…”

Section: Introductionmentioning

confidence: 99%

Effects of Retarding Admixture, Superplasticizer and Supplementary Cementitious Material on the Rheology and Mechanical Properties of High Strength Calcium Sulfoaluminate Cement Paste

2020

ACT

In this paper, the effects of retarding admixture, polycarboxylate (PCE) superplasticizer and supplementary cementitious material (SCM) on the rheology of high strength calcium sulfoaluminate (CSA) cement paste are investigated. At the water to binder ratio of 0.3, one PCE, two retarding admixtures, and three SCMs were used in the test. The test results show that much more PCE is needed for paste with citric acid than that with sodium borate to achieve a similar initial flowability. The reference paste and pastes mixed with sodium borate or fly ash exhibit shear thickening; pastes mixed with citric acid or silica fume exhibit shear thinning. The addition of citric acid increases the maximum shear stress of pastes, while the maximum shear stress can be significantly reduced by silica fume. Both the retarding admixtures and SCMs will strongly reduce the early-age compressive strength of the cement paste. At 28 days of age, CSA cement paste incorporating retarding admixtures has comparable strength to the reference paste. Silica fume has less negative effect on the compressive strength of the CSA cement paste due to the significant filling effect.

“…Other mineral compositions in SRC are similar to OPC, so the SRC mortar also suffered from the formation of gypsum and thaumasite and it showed limitedly better resistance to sulfate attack at low temperature than the OPC mortar. The main minerals of sulphoaluminate cement are C 4 A 3Š , C 2 S, and C 12 A 7 , and their hydration products mainly contain ettringite, CSH gel, and Al(OH) 3 [15]. Very strong peaks corresponding to ettringite and weak peaks attributed to portlandite can be found in the XRD pattern of the SAC mortar.…”

Section: Mineralogymentioning

confidence: 99%

Influence of Cement Type and Water-to-Cement Ratio on the Formation of Thaumasite

Advances in Materials Science and Engineering

2017

Cement mortar prisms were prepared with three different cement types and different water-to-cement ratios plus 30% mass of limestone filler. After 28 days of curing in water at room temperature, these samples were submerged in 2% magnesium sulfate solution at 5 ∘ C and the visual appearance and strength development for every mortar were measured at intervals up to 1 year. Samples selected from the surface of prisms after 1-year immersion were examined by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results show that mortars with sulfate resisting Portland cement (SRC) or sulphoaluminate cement (SAC) underwent weaker degradation due to the thaumasite form of sulfate attack than mortars with ordinary Portland cement (OPC). A lower water-to-cement ratio leads to better resistance to the thaumasite form of sulfate attack of the cement mortar. A great deal of thaumasite or thaumasite-containing materials formed in the OPC mortar, and a trace of thaumasite can also be detected in SRC and SAC mortars. Therefore, the thaumasite form of sulfate attack can be alleviated but cannot be avoided by the use of SAC or SRC.