| The impact of slag on the hydration of cement in the view of dilution and nucleation effect were studied by hydration heat and electrical resistivity in this paper.The reaction characteristics of calcium hydroxide-slag paste were used to analyze the pozzolanic reaction of slag in slag-cement pastes by SEM,TG/DSC and other testing methods.The hydration characteristic parameters of electrical resistivity,shrinkage and hydration heat as well as their correlations for slag-cement pastes were also analyzed in 3d.The research results were as follows.(1)Two indexs were proposed to describe slag effect.The dilution effect indexes and crystal nucleus effect indexes of slag at 72 h were 1.03,1.11,1.13 and 1.01,1.04,1.10 respectively for the slag-cement pastes at a constant water-binder ratio(W/B)of 0.5 with different slag dosages(10%,20%,30%).The increase of the dosage of slag means the increase of W/B and the larger area for the deposition of hydration products.The hydration processes of cement were promoted and both of two indexes increased with the increasing dosage of slag.(2)The required content of calcium hydroxide was 0.058 g/g to 0.14 g/g for the completely reaction of slag.The reaction activity could be effectively activated when the mass of calcium hydroxide reached the 5% of slag.The increase of the calcium hydroxide promoted the reaction process of slag and the reaction products observed by SEM were principally fibrous C-S-H gel.(3)The electrical resistivity of the slag-cement pastes increased in the dissolution period and decreased in the hardening period due to the addition of slag.Increasing the dosage of slag was adversed to the reduction of the porosity.The addition of slag also delayed the occurrence of the two peaks in the differential curves of the electrical resistivity as well as the time that the pastes stepped into the hardening deceleration period.The initial tortuosity of the blended pastes at a constant W/B of 0.5 were higher than that of cement paste and reached the maximum of 1.25 when the dosage of slag was 20% calculated by electrical resistivity method.(4)There was a good correlation between the electrical resistivity and the cumulative hydration heat which could be expressed by the equation: Q=kln(?)+b.The value of k firstly increased from 152.3 to 170.2 and then decreased to 147.9 while the value of b value increased from 37.93 to 82.31 with the dosage of slag.The value of k was closely related to the hydration process in the blended pastes and mainly influenced by the chemical properties of mineral admixtures.The value of b was closely related to the state of the fresh pastes and mainly influenced by the physical properties of mineral admixtures.(5)The autogenous shrinkage(AS)of the pastes at the W/B of 0.3 and 0.4 decreased with the increasing the dosage of slag.Compared with the cement paste,the AS of blended pastes with 30% mass of slag at 72 h were reduced by 25.44% and 15.18% respectively.The AS of the pastes at the W/B of 0.5 increased with the increasing the dosage of slag at 72 h and increased by 23.46% for the blended paste with 30% mass of slag compared with the cement paste.The drying shrinkage of the pastes at the W/B of 0.3,0.4 and 0.5 decreased with the increasing the dosage of slag at 72 h and decreased by 23.86%,28.49% and 23.86% respectively compared with the cement pastes. |
PDF Full Text Request