Cement paste autoclaved

Fig. 8.8 Relations between compressive strength (log scale) and porosity data from various sources for Portland cement pastes cured at ordinary temperatures (open circles), hot pressed Portland cement paste (filled circle), autoclaved pastes of Portland cement, sometimes with added sulphur (filled squares) and autoclaved pastes of Portland cement with 50% (open squares) or 30"/o (cross) of added pfa. After Feldman and Beaudoin (F36).

PROPERTIES OF AUTOCLAVED CEMENT PASTE CONTAINING SCRAP FRP POWDER... 

Cement paste specimens 40x40x 160mm were molded, and subjected to autoclave cure (160°C, lOhr.) after 7 days in 20°C, 85%R.H. 

According to JIS R 5201, the autoclaved cement paste specimens were tested for flexural and compressive strengths, and their bulk specific gravity were also measured. 

The conclusion obtained from the test results on the properties of autoclaved cement paste containing scrap FRP or glass powder are summarized as follows. 

The higher differences, in phase composition are observed in the pastes autoclaved in the saturated water vapour at temperature range 120-200 °C. The phase composition of the calcium sihcate hydrates is primarily the function of C/S in the starting mixture. In Portland cement paste without additions the C-S-H (I) is transformed quickly to the C-S-H (II) and the latter already at 25 °C into a-C2SH [194, 199]. The proper addition of the ground quartz gives the 1.1 nm tobermorite. This phase contains aluminium in solid solution, which causes the transition to xonotlite, at temperatures exceeding 160 °C difficult... 

Feldman and Beaudoin correlated strength and modulus of elasticity for several systems over a wide range of porosities. The systems included pastes hydrated at room temperature, autoclaved cement paste with and without additions of fly ash, and those obtained by other workers. Porosity was obtained by measurement of solid volume by a helium pycnometric technique and apparent volume, through the application of Archimedes principle. 

Xonotlite is an important phase, because it is dominating component in the materials autoclaved at higher temperatures (Fig. 4.53), as well as formed in the pastes in deep wells cementing. 

To determine experimentally whether a hardened paste made from a cement with a given amount of MgO will preserve its volrrme stability indefmitely, accelerated testing has to be performed. In such tests the test specimens are exposed to an autoclave treatment, and the expansion that takes place rmder these conditions is assessed. 

Klimesch, D.S. et al. (1998) Metakaohn additions in autoclaved cement-quartz pastes a 2 Si and Al MAS NMR investigation. Advances in Cement Research 10,93-99. 

It is known from the past that hydrates leach from concrete. Taylor [21] has proposed various measures against leaching by using Pozzolanic materials, alumina cement, dense concrete, carbonated concrete, autoclave curing, and so on. Even ancient concrete used 5000 years ago in China [22] did not use steel the cement close to today s low-heat Portland cement had carbonated, and had helped to maintain the long-term soundness of the material. Based on such information, the leaching resistance of carbonated concrete and Pozzolan material was evaluated. The dissolution equilibrium relationships... 

It has also been reported that the second derivative DTA is more useful to examine the products formed during the autoclaving of cement-quartz-metakaolin mixtures. Klimesch and Rayt ] subjected a mixture of quartz (38.5%) and cement (61.5%) containing different amounts of metakaolin and autoclaved them for 8 hrs at 180°C. It was found that the second derivative differential thermal curve provided a more detailed information, particularly in temperatures of 800-1000°C. In Fig. 35, DTA and second derivative curves for cement-quartz-metakaolin pastes are compared. The exotherms occur at 840, 903, and 960°C due to the formation of wollastonite from C-S-H, aluminum-substituted tobermorite, and anorthite from the hydrogamet residue respectively. The small endot-herm at 828°C preceding the first exotherm is probably caused by well crystallized calcite. 

Klimesch, D. S., and Ray, A., Use of Second Derivative Differential Thermal Curve in the Evaluation of Cement-Quartz Paste with Metakaolin Addition, Autoclaved at 180°C, Thermochimica Acta, 307 167-176 (1997)... 

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