Abstract:The development of free deformation and internal moisture in cement paste, mortar and concrete were experimentally investigated. The results show that the deformations of cement paste, mortar and concrete at early age all exhibit plastic swelling at initial several hours after casting and then shrinking with a gradually reduced rate. The end point of swelling may be corresponding to the transformation point of plastic state to solid state and this point can be defined as setting time of the cement based materials. The development of shrinkage starting from setting point of the three kinds of cementitious materials exhibits at first a fast developing stage(stage Ⅰ) and is followed by a relatively slow developing stage(stage Ⅱ). The restraint effect of aggregates on shrinkage is significant only in the stage Ⅱ. In stage Ⅰ a similar shrinkage values are observed on the three kinds of materials. The development of moisture inside cement paste, mortar and concrete can be described as a vapor saturated stage with saturated moisture followed by a stage in that internal moisture is gradually reduced. The shrinkage developed within stage Ⅱ can well correlate to the reduction of internal moisture.

Abstract:Effect of decalcification on microstructure of CSH gel in ASTMⅠcement paste were studied by Xray fluorescence spectrometer(XRF), Xray diffraction(XRD), infrared spectroscopy with Fourier transform(FTIR) and 29Si MAS NMR with deconvolution technique. It is shown from test results that the decalcification process can be divided into two stages. When the molar ratio of CaO to SiO2 in the pastes at 3, 28d is lowered from~2.78 to~2.00, almost all of CH is removed and CSH gel is partially decalcified, the average chain length(ACL) of CSH is increased from 2.4 to 4.4 for 3d paste and from 2.9 to 5.8 for 28d paste respectively, and I(Q2)/I(Q1) is also increased. While the molar ratio of CaO to SiO2 in the pastes comes to~1.83, decalcification of CSH gel occurs. CSH polymerizes and I(Q2)/I(Q1) increases largely in this stage, which results in further increase of ACL to 6.2 for 3d paste and 9.9 for 28d paste. The mechanism of increase of CSH polymerization could be transformation of dimeric CSH toward highly polymerized CSH. However, Al doping could affect the stability of CSH microstructure. In molecular level, the existence of the pure bridging siliconoxy tetrahedrons in CSH is beneficial to the optimization of the microstructure.