Cement paste volume

The concrete volume increase is directly dependent of the cement paste volume change. 

Fig. 20.5. Concrete is a particulate composite of aggregate (60% by volume) in a matrix of hardened cement paste.

Here, V and 1/ are the volume fractions of aggregate and cement paste, and E and E are their moduli. As Fig. 20.6 shows, experimental data for typical concretes fit this equation well. 

A concrete consists of 60% by volume of limestone aggregate plus 40% by volume of cement paste. Estimate the Young s modulus of the concrete, given that E for limestone is 63 GPa and E for cement paste is 25 GPa. 

The T) and T2 dependence is described by Eqs. (3.4.3) and (3.4.4) [34] where Qi and q2 are spin-lattice and spin-spin surface relaxivity constants, and S/ Vis the surface-to-volume ratio of the pore. These equations provide the basis of a methodology for crack detection in cement paste specimens [13]. 

Economies in mix design are effected by reducing the cement content whilst maintaining the same water-cement ratio. In view of the reduction of paste volume, conflicting recommendation are made of how this should be compensated for. The following is a guide [84] ... 

Volume deformations are largely a function of the nature and quantity of the cement paste in the concrete and it has been shown [113] that studies on... 

Fig. 47 Volume changes of cement pastes under near saturated conditions (Morgan).

The apparatus shown in Fig. 3.5 was used, and was filled completely with cement paste. Admixture additions were made by injecting with a hypodermic needle through the rubber cap. Pastes prepared in this way had air contents of less than 0.6% by volume, were free from any premature stiffening tendencies and were homogeneous. 

Fig. 5.23 Pore volume distribution of cement pastes from nitrogen adsorption. Curve 1 = cement with no admixture curve 2 = cement paste and 2% CaCl2 (Gouda).

Portland cement pastes. Influence of composition on volume constancy and salt resistance. Ind. Eng. Chem., 26 1049-1060. 

Table 7.3 Calculated mass balance and compositions by weight and by volume for a 14-month-old cement paste (w/c = 0.5) Percentages on the ignited weight for material equilibrated at 11% RH... 

The content of non-evaporable water, relative to that in a fully hydrated paste of the same cement, was used as a measure of the degree of hydration. Portland cement paste takes up additional water during wet curing, so that its total water content in a saturated, surface dry condition exceeds the initial w/c ratio. Evidence from water vapour sorption isotherms indicated that the properties of the hydration product that were treated by the model were substantially independent of w/c and degree of hydration, and only slightly dependent on the characteristics of the individual cement. The hydration product was thus considered to have a fixed content of non-evaporable water and a fixed volume fraction, around 0.28, of gel pores. 

Fig. 8.5 Relations between porosities (volume percentages) and water/ccmcnt ratio for mature Portland cement pastes. The experimental data are for pastes at least 8 months old, and the calculated curves relate to a typical cement aged 18 months. Open symbols total water porosities. Filled or half-filled symbols mercury porosities. Curve A total water porosity. Curve B free water porosity. Curve C capillary porosity. References to data O (P20) O (S77) A (F33) V (M68) (S78) (F34) 9 (019) (M68) (D3I) 3 (H4I). In the last two cases, porosities by volume were estimated from data referred in the original sources to masses of dried paste, assuming the tatter to have contained 0.23 kg of water per kg of cement having a specific volume of 3.17 x 10 m kg h...

In Section 7.3.3, a method was described for calculating the quantitative phase composition of a cement paste by weight and by volume for various drying conditions. Fig. 8.5 includes porosities thus calculated for 18-month-... 

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