In this study, first of all, the atomistic structure of cement hydration products is estimated via molecular dynamics method and their elastic properties are extracted. Then, cement hydration simulation is done by HYMOSTRUC3D model and the obtained results from both molecular dynamics and HYMOSTRUC3D methods are used for simulation in macro-scales through analytic and lattice methods. Finally, elastic properties of cement paste are estimated with two mentioned methods and compared with each other and also with literature. The study, in fact, aims to investigate an appropriate multi-scale simulation model to examine cement paste elastic properties.

Graded blended cement made of graded Portland cement (PC), blast furnace slag (BFS) and fly ash (FA) is attractive for cement production. For manufacturing graded blended cement, a suitable mathematical expression should be introduced to describe the particle size distribution (PSD) of its components and control the quality of graded blended cement. This study aims to evaluate Rosin-Rammler-Sperling-Bennet (RRSB) distribution and lognormal distribution for describing the PSD of the components of graded blended cement. RRSB distribution and lognormal distribution are used to fit the PSD of ungraded and graded PC, BFS and FA. It is found that lognormal distribution exhibits smaller fitting errors for describing the PSDs of graded PC, BFS, FA and ungraded FA. What is more, lognormal distribution exhibits good simplicity and popularity. Hence, it is recommended to use lognormal distribution to control the PSD of graded blended cement in manufacturing process.

Because the pore plays the primary role in strength development of blended cement paste, the role of filler-hydrates adhesion properties has attracted very little attention. The purpose of this study is to investigate the effect of filler-hydrates adhesion properties on strength development of cement paste. In this study, the development of compressive strength of portland cement paste and cement paste blended with limestone powder and micronized sand was studied experimentally. Parallel with this experimental study, the contact area in these cement pastes was quantified numerically. The relationship between the measured compressive strength and simulated contact area was then analyzed. With this relationship, the effect of filler-hydrates adhesion properties on strength development of cement paste was quantified. The contact area between hydrating cement particle and micronized sand particle had no contribution to the compressive strength. In contrast, the contact area between the hydrating cement particle and limestone particle had a substantial contribution to the compressive strength.

Mercury intrusion porosimetry (MIP) measurements are widely used to determine pore throat size distribution (PSD) curves of porous materials. The pore throat size of porous materials has been used to estimate their compressive strength and air permeability. However, the effect of sample size on the determined PSD curves is often overlooked. In pursuit of a better understanding of the effect of sample size on mercury intrusion into porous materials, a combined experimental and numerical approach was applied. Quartz sand and epoxy resin were mixed to form artificial sandstone. Digital microstructures of the sandstone were obtained by using X-ray computed tomography (CT scan) technique. PSD curves of the artificial sandstone with different sample sizes were determined both by MIP measurement and by simulation of mercury intrusion (i.e., MIP simulation). Percolation analysis was performed on mercury-intruded pores in the digital microstructures. The PSD curves determined both by MIP measurements and by MIP simulations show that there was a significant effect of sample size on mercury intrusion before percolation of mercury-intruded pores. The effect of sample size decreased with the increasing pressure. After the mercury-intruded pores percolated through the samples, the effect of sample size on mercury intrusion became minor. The pore throat size of the artificial sandstone was used to estimate the air permeability using the relation proposed in the literature. The calculated air permeability of the smaller sandstone sample was higher. However, in principle, the air permeability of sandstone samples should be independent of the sample size. Two main conclusions can be drawn: (1) a fixed sample size should be used in MIP measurements or MIP simulation so that the PSD curves of different samples can be properly compared, (2) sample size needs to be considered when the pore throat size determined by MIP measurement is used for estimating air permeability.

More and more studies are based on digital microstructures of cement pastes obtained either by numerical modelling or by experiments. A comprehensive understanding of the their pore structures, therefore, becomes significant. In this study, the pore structure of a virtual cement paste (HYMO-1d) generated by cement hydration model HYMOSTRUC 3D is characterized. The pore structure of HYMO-1d is compared to the one of CT-1d that is reconstructed by using X-ray computed tomography technique (CT scan). Both HYMO-1d and CT-1d have the same porosity. Various parameters are taken into account, viz., the specific surface area, the pore size distribution (PSD), the connectivity and the tortuosity of water-filled pores. Regarding the PSD, two concepts (i.e., the “continuous PSD” and the “PSD by MIP simulation”) are adopted. The “continuous PSD” is believed to be a “realistic” PSD; while the “PSD by MIP simulation” is affected by the “throat” and “ink bottle” pores. The results show that HYMO-1d and CT-1d exhibit a similar curve of “continuous PSD”, but distinct curves of “PSD by MIP simulation” and different specific surface areas. A lower complexity of the pore structure of HYMO-1d is indicated by a higher tortuosity of water-filled pores with reference to CT-1d. This study indicates that the comparison of pore structures between the digital microstructures should be based on multiple parameters. It also gives an insight into further studies on digital microstructures, i.e. transport properties of unsaturated materials.

Autogenous shrinkage is the volume deformation of a closed, isothermal, cementitious material system not subjected to external forces. How to accurately predict the autogenous shrinkage in hardening cement-based materials is an important issue in concrete technology because autogenous shrinkage increases cracking risk and reduces the durability and service life of reinforced concrete structures. Many models simulated the autogenous shrinkage of cement-based materials based on some mechanisms such as capillary pressure and disjoining pressure. These models are normally empirical and cannot reveal the deformation behavior of cement-based materials under the internal load of the driving force of autogenous shrinkage in microscale. As a consequence, the reliability of these models are questionable. This paper proposes a numerical model to simulate the autogenous shrinkage of hardening cement paste. A cement hydration and microstructure model HYMOSTRUC3D is used to simulate the microstructure of cement paste. A pore morphology based method is applied to describe the water and empty capillary pores distribution in the microstructure. Capillary pressure in the microstructure of cement paste is calculated from relative humidity measured by experiment based on Kelvin equation. A discrete algorithm is proposed to divide the hydration time into several static times. At each static time, a lattice finite element fracture method is used to simulate the deformation of simulated microstructure of cement paste under capillary pressure imposing. The autogenous shrinkage of hardening cement paste is equal to the sum of deformation of cement paste at each static time. The autogenous shrinkage of Portland cement paste with water to cement ratio of 0.3 is predicted. The simulation results are in a good agreement with experiments.