Drying Shrinkage Of Cement Paste Research Articles

Modeling the Drying Shrinkage of Cement Paste Prepared with Wastewater

Modeling the Drying Shrinkage of Cement Paste Prepared with Wastewater

Is early drying shrinkage still determined by the mesopore content? A case study of cement paste with minerals

Long-term drying shrinkage is deemed to be relevant with the mesopore content of cement paste, so is early drying shrinkage still determined by the number of mesopores? This was not the case. Through combining the measurement of water loss and pore size distribution (PSD), this study provides an explanation of early-age drying shrinkage of cement paste with different types/contents of minerals (i.e., blended cement paste) added, and a corresponding prediction model was proposed in terms of its early shrinkage. The results show that during hydration, instead of the mesopore content, the water loss due to evaporation in capillary pores of cement paste was well correlated with its early drying shrinkage, which could be attributed to a small portion of mesopores rather than all mesopores have lost water at an early age. Meanwhile, a parameter rs, which was defined as the radius of the pores where the meniscus formed, was calculated by combining the results of PSD and water evaporation, and its reduction led to an increment of drying shrinkage of specimens. Finally, the outcomes obtained from the proposed prediction model fitted well with experimental data, revealing the effectiveness and accuracy of the model in foreseeing early drying shrinkage of blended cement paste.

Influences of the dosage of dolomite powder on the fracture properties and volume stability of cement-based materials

The effects of dolomite powder dosage on the fracture properties and volume stability of cement-based materials were investigated by three-point bending method and corrugated tube method, respectively. The experiment results showed that the fracture toughness of cement mortar incorporating dolomite powder was raised compared to that of reference cement mortar. After dolomite powder was added into cement paste, the improvement of fracture toughness, flexure, and compressive strength was observed due to the formation of a new phase (magnesium hydroxide and calcium carbonate) combined with the nucleation and physical filling effect. Autogenous shrinkage of samples incorporating dolomite powder were higher than that of the control samples because the addition of dolomite powder increased the surface tension of water in pores and the compression on the walls of capillary pores, facilitating higher autogenous shrinkage. Drying shrinkage of cement pastes blended with dolomite powder was lower than that of the control samples. The refinement of the pore structure of samples incorporating dolomite powder decreased the internal capillary pressure, causing smaller drying shrinkage.

Influence of Superplasticizer Type and Dosage on Early-age Drying Shrinkage of Cement Paste with Consideration of Pore Size Distribution and Water Loss

We introduced a parameter rs (the radius of the pores where the meniscus forms), which is composed of two factors, i e, water loss and cumulative pore size distribution (PSD), to provide a better explanation of the influence of superplasticizers(SPs) on early-age drying shrinkage. In our experiments, it is found that the addition of three types of SPs leads to a significant increase in the early-age drying shrinkage of cement paste, and drying shrinkage increases with the dosage of SPs. Based on the results above, we further studied the mechanism of the effects of SPs on the early-age drying shrinkage of cement paste by PSD and water loss, which are two components of rs. The experimental results indicate that rs can be a better index for the early-age drying shrinkage of cement-based materials with SPs than a single factor. In addition, the effects of SPs on other factors such as hydration degree and elastic modulus were also investigated and discussed.

Influence of evaporation rate on pore size distribution, water loss, and early-age drying shrinkage of cement paste after the initial setting

The influence of the water evaporation rate on early-age drying shrinkage of cement paste is investigated. To measure shrinkage, three mixed groups with different water–cement ratios (w/c’s) were studied over a period of 72 h. The 72-h early-age drying shrinkage, starting from the initial setting time, was measured. The pore size distribution (PSD) was measured using mercury intrusion porosimetry. The results show that the increase of the evaporation rate leads to a large increase in the early-age drying shrinkage. During the first six hours, each group had a good positive relationship between the shrinkage ratio and water loss ratio, and the shrinkage ratio was slightly greater than water loss ratio. Different water evaporation rates influence the most probable pore diameter of cement paste, which increases as the water evaporation rate increases. However, the porosity of the bulk paste and volume of mesopores was not consistent with the rule of the most probable pore diameter. A higher water evaporation rate resulted in a lower pore volume within 26 nm. Therefore, a parameter rs, which can explain the contradiction between the increase of shrinkage and volume of mesopores, was calculated from the water loss and cumulative PSD. The total volume of mesopores may not be the dominant factor in early-age shrinkage, but the most probable pore diameter, parameter rs, and relationship between them can provide a better index of drying shrinkage for the early-age of cement-based materials. Furthermore, in the paste with a w/c of 0.28, rs and drying shrinkage show a linear relationship.

Mechanism Research of Drying Shrinkage of Cement Pastes Based on the Contact Angle

Capillary tention is one of the driving forces of shrinkage of cement-based materials, which is related to distribution of pore size, surface tension of pore water, contact angle of pore walls and so on. There are some appropriate test methods for pore diameter and surface tension of cement-based materials, but the contact angle of pore water is rarely related to. This paper showed a new method to test the contact angle of cement-based materials which is based on the principle of thin-layer wicking about surface physical chemistry. Combining Washburn equation x2=(Refft/2) , the contact angle of analog pore solution to cement paste was obtained. The influence of superplasticizers and mineral admixtures on the contact angle and drying shrinkage of cement pastes also were researched. The results showed that the larger contact angle leads to the smaller surface tension of pore solution, which also caused that the capillary wall wass infiltrated more difficultly. As a result, the pressure of pore and the drying shrinkage were both small, vice versa.

Optimization of self-compacting filling grout mixtures for repair purposes

Today self-compacting filling grouts (SCFG) are preferred for rapid repair purposes due to the application easiness, in addition to physical and mechanical advantages. However for self-compactability, the paste phase must meet some certain criterion at fresh state. To reach the optimum mix design for SCFG, it is important to find out the right combination of cement and filler material, both amount and type. The successful utilization of quarry dust in self-levelling cement pastes could turn this waste material into a valuable resource.In this research, the effect of cement replacements with three types of limestone powders produced from different quarries on the rheology of the fresh SCFGs has been studied. Also the mechanical and drying shrinkage properties of SCFGs have been investigated. A 10% replacement of cement with a special type of quarry dust was found to lead the best performance at fresh state rheological properties and at hardened state compressive strengths and drying shrinkage. All filler additions decreased the drying shrinkage of cement pastes at different orders when compared with pure cement paste specimens. The positive effects of quarry dust on fresh and hardened properties of self-levelling binders make this material a feasible additive besides its economical and environmental advantages.

Drying shrinkage of cement paste as measured in an environmental scanning electron microscope and comparison with microstructural models

A recently developed image-intensity-matching technique has been used to analyse images of cement paste which were dried in an environmental scanning electron microscope. Shrinkage that occurs during changes in relative humidity is reported, together with some of the influences of water-to-cement ratio, temperature and age. Results from microstructurally based models are compared with experimental results. The best fit of models to experiment is achieved if calcium silicate hydrate (C–S–H) is divided into two types: high density C–S–H, which does not shrink, and low density C–S–H, which does shrink. Approximate values of unrestrained shrinkage of the low density C–S–H are attained as a function of relative humidity.

Drying shrinkage of cement paste and concrete: A reappraisal of the measurement technique and its significance

Drying shrinkage of cement paste and concrete: A reappraisal of the measurement technique and its significance