The1HT 1 study of the influence of clay addition on Portland cement hydration

Abstract

Effects of addition of three standard clay minerals, Na-montmorillonite, illite and kaolinite, on Portland cement hydration properties were studied. The IH spin-lattiee relaxation of exchangeable water was monitored during hydration time and the data were processed by spin-grouping analysis. The values and evolution dynamics of both resolved T l eomponents and corresponding magnetization fractions show that each day mineral lowers the fluidity of Portland cement paste and accelerates its hydration in dormant. In advanced stages of hydration, the Na-montmorillonite provŸ the accelerating influence, while the kaolinite exhibits the retarding effect. The final values of gel pores to capillaries pereentage fractions ratio indieate a slightly lower porosity of samples with Namontmorillonite anda higher porosity of pastes with the same percentage of illite or kaolinite, regarding to the pure hardened Portland cement.

Microstructure engineering of Portland cement pastes and mortars through addition of ultrafine layer silicates

“…For example, it has been observed that prolonged drying decreases the surface area [34,35]. Samples are dried prior to adsorption, e.g., by D-drying for periods as long as 3 weeks [17]. Rarick et al [35] found that the nitrogen surface area of Portland cement paste decreased with storage time after D-drying which they tentatively attributed to carbonation.…”

“…Micro-or nano-sized layer silicates exhibit no pozzolanic reactions in Portland cement systems [15]. However, addition of these silicates to Portland cements accelerates the cement hydration [15][16][17] by increasing the degrees of hydration for both alite and belite [17]. Moreover, it has been shown that replacement of 20 wt.% of the Portland cement by a kaolinite or illitic clay results in an increased porosity of paste samples, but a decreased porosity of mortars as measured by mercury intrusion porosimetry [18].…”

Effects of Mud Content on the Setting Time and Mechanical Properties of Alkali-Activated Slag Mortar

“…Consequently, the rate of breaking the Ca-O, Si-O-Si, and Al-O-Al bonds is sped up, which leads to the increase in Ca 2+ ion concentration and accelerates the formation of hydration products and the arrival of the initial setting state [20,46,47]. However, the water absorption of mud also delays the hydration process, especially with high kaolinite content [48][49][50][51], leading to a longer final setting time. As for the effect of the particle sizes of mud on setting time, the capability of liquid absorption of clay with a smaller particle size is stronger than that of silt with a larger particle size [46].…”

“…When the silt and clay content is less than 4%, the mud has almost no effect on the compressive and flexural strengths of AAS mortar, which is because the mud fills the pores of the sand skeleton [52] and reduces the negative effect caused by the addition of mud. When the mud content exceeds 4%, the compressive and flexural strengths of AAS mortar decrease rapidly, mainly for the following reasons: (1) mud absorbs water from the fresh mortar and this affects the hydration process [49][50][51];…”