Shrinkage Of Cement Paste Research Articles

Relationship between buck electrical resistivity and drying shrinkage in cement paste containing expansive agent and mineral admixtures

The buck electrical resistivity, drying shrinkage, mass loss rate and compressive strength are investigated in cement-based materials at early age with a fixed water-binder ratio and constant expansive agent content, considering the effects of different fly ash and slag replacements of cement. Moreover, microstructure of the matrix was analyzed by scanning electron microscope (SEM). The results showed that the specimens with fly ash presented higher buck electrical resistivity and mass loss rate and lower drying shrinkage, due to their loose structure and large expansion behavior generated by more ettringite crystals. Two stages in buck electrical resistivity and three stages in drying shrinkage were defined according to the continuous cement hydration and water evaporation. A natural logarithm relationship between buck electrical resistivity and drying shrinkage in cement paste was constructed. Therefore, electrical response measurement can be applied to characterize the drying shrinkage behavior of cementitious materials.

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.

Effect of Supplementary Materials on the Autogenous Shrinkage of Cement Paste.

In recent years more and more attention has been given to autogenous shrinkage due to the increasing use of high-performance concrete, which always contains supplementary materials. With the addition of supplementary materials—e.g., fly ash and blast furnace slag—internal relative humidity, chemical shrinkage and mechanical properties of cement paste will be affected. These properties significantly influence the autogenous shrinkage of cement paste. In this study, three supplementary materials—i.e., silica fume, fly ash and blast furnace slag—are investigated. Measurements of final setting time, internal relative humidity, chemical shrinkage, compressive strength and autogenous deformation of the cement pastes with and without supplementary materials are presented. Two water-binder ratios, 0.3 and 0.4, are considered. The effects of different supplementary materials on autogenous shrinkage of cement paste are discussed.

Early-age shrinkage of cement pastes with polypropylene and curaua fibres

The aim of this research was to investigate the effect of the addition of discrete polypropylene fibres (PPF) and curaua fibres (CF) on the early-age autogenous and drying shrinkage of cement pastes. The fibres used were 12 mm long and the volume fraction varied from 0.3 kg/m3 (0.03%) to 2.7 kg/m3 (0.30%). Autogenous, unrestrained and restrained drying shrinkage tests were performed and it was found that the addition of these fibres influenced the different shrinkage behaviours. A significant reduction in autogenous shrinkage was observed in the specimens with 2.7 kg/m3 of CF, especially in the first few hours of curing. Regarding the unrestrained drying shrinkage, the addition of 2.7 kg/m3 of CF led to only a slight improvement (by about 8.5%) and lower fibre contents had little or no influence. The addition of PPF slight reduced the unrestrained drying shrinkage (by about 8.13%) for all the evaluated fibre contents. Both fibres delayed the development of cracks and reduced crack opening during the restrained drying tests. The addition of 2.7 kg/m3 of PPF or CF delayed cracking by 23% and 18%, respectively. The results indicate that discrete CF can be potentially used to restrain the autogenous and drying shrinkage of cementitious materials.

Modeling autogenous shrinkage of hydrating cement paste by estimating the meniscus radius

In this study, a model for predicting the autogenous shrinkage of hydrating cement paste was developed by estimating the radius of meniscus, which varies with age. The meniscus radius was estimated by considering the pore structure that varies with age, and the amount of water consumed by the hydration reaction. The proposed model was verified through a comparison with test data, with respect to the self-desiccation estimated from the meniscus radius and autogenous shrinkage of cement paste with different water-to-cement ratios. While considering poroelastic behavior, the proposed model predicted autogenous shrinkage of cement paste with reasonable accuracy. It was shown that the amount of water consumed by the hydration reaction increases the autogenous shrinkage; however, the pore structure has a greater effect on the magnitude of autogenous shrinkage. The proposed model is expected to be useful in predicting autogenous shrinkage of concrete without measuring the internal relative humidity.

Effect of different wind speeds and sealed curing time on early-age shrinkage of cement paste

The influence of different wind speeds and sealed curing time on early-age shrinkage of cement paste was investigated. The 72-h early-age total shrinkage of cement paste after sealed curing for 0 h, 3 h, 6 h, 9 h, 12 h, and 24 h starting from the initial setting time under different wind speeds was studied. Water loss, autogenous shrinkage, tensile strength, pore size distribution (PSD) and hydration degree were measured. Elastic modulus, cracking strain, and radius of the pores where the meniscus forms were calculated based on the data obtained. For mixtures that did not undergo sealed curing, the wind speed could considerably increase the drying shrinkage and total shrinkage of the cement paste. The wind speed also reduced the early tensile strength, hydration degree, and elastic modulus of the cement paste. Within 1 day, the cracking strain was reduced by wind speed. According to the experimental data, a fitting formula for the early total shrinkage of cement paste is proposed, and the wind speed influencing factor βw is also proposed for the first time. Considering the PSD and water loss to study the mechanism of early drying shrinkage of cement paste, we found that there is a good correlation between rs and drying shrinkage. The exponential formula is given between rs and drying shrinkage. For mixtures with sealed curing, the total shrinkage and water loss decreased with increasing sealed curing time. However, the effects of water loss at different stages on drying shrinkage were different. Water evaporation in the early stage led to more drying shrinkage than water evaporation in the later stage. Sealed curing also weakened the increasing effect of wind speed on total shrinkage, so that at the same wind speed, the shrinkage increment was considerably reduced. After analysis and comparison, it was found that it is economical and reasonable to adopt sealed curing for 6 or 9 h, which can effectively decrease the early total shrinkage and improve the cracking strain of the cement paste in the wind environment.

Synthesis of a New Polycarboxylate at Room Temperature and Its Influence on the Properties of Cement Pastes with Different Supplementary Cementitious Materials

Three polycarboxylates with different comb structures (i.e., the same degree of polymerization in side chains but different main chains) were synthesized via radical polymerization reaction at room temperature. The effect of polycarboxylates on the surface tension and the flowability in cement pastes was determined. The best product was selected to study its effects on the hydration heat evolution, compressive strength, autogenous shrinkage, and drying shrinkage of cement pastes with different kinds and contents of supplementary cementitious materials. The results showed that with the increase of molar ratio between AA and TPEG to 6 : 1, we could synthesis the best product. When the water‐binder ratio was 0.4, with the increase of polycarboxylates, the cement hydration heat evolution had been slowed down, and the more the dosage was, the more obvious the effect was. Adding supplementary cementitious materials to cement under the same experimental conditions also played a mitigation role in slowing down the hydration heat. When the water‐binder ratio was 0.3, supplementary cementitious materials could increase the strength of cement by 24.5% in maximum; its autogenous shrinkage and drying shrinkage could be decreased, respectively, by 60.1% and 21.9% in the lowest.

Prediction of autogenous shrinkage of cement pastes as poro-visco-elastic deformation

Precise and robust predictions of autogenous shrinkage of high performance concrete are essential to limit self-induced stresses and cracking in modern concrete structures. This paper presents predictions of autogenous shrinkage for three cement pastes of different compositions by considering first only the poro-elastic deformation and then including also the poro-visco-elastic response. This study used experimentally-determined parameters for the material properties of both the elastic and the visco-elastic components, which ensured the reliability of the calculations. The prediction of the poro-visco-elastic response of the material to the internal stress was performed using a generalized Kelvin-Voigt model that also considered aging. It is found that, while the poro-elastic calculations systematically underestimates the measured shrinkage, predictions with the inclusion of the viscous response overestimates the shrinkage.

Novel low-cost shrinkage-compensating admixture for ordinary Portland cement

This work proposes a low-cost and eco-friendly shrinkage-compensating admixture (SCA) composed of an Al-rich waste and calcium sulfate for cement-based binders. The hydration process and microstructural changes of cement pastes with the proposed SCA were investigated by means of isothermal conduction calorimetry, X-ray diffraction, differential thermal and thermogravimetry analysis, elastic modulus and compressive strength tests for several hydration times. Length changes were also followed for 7 days. The main results revealed that the cement pastes with the proposed SCA expand between the first and third day of hydration enough to mitigate the shrinkage of cement pastes. SEM micrographs and X-ray patterns suggest that the expansion is managed through the nucleation and growth of needle-like crystals of ettringite.

Combined effects of biochar and MgO expansive additive on the autogenous shrinkage, internal relative humidity and compressive strength of cement pastes

Internal curing and expansive additives are normally used to mitigate the autogenous shrinkage of cement materials. Biochar, with a porous microstructure and water holding capacity, has a potential to be used as a novel internal curing agent, whereas few work was focused on its impact on the autogenous shrinkage of cement materials. The present work aims to investigate the effects of biochar and its combination with MgO expansive additive (MEA) on the internal relative humidity, autogenous shrinkage, compressive strength as well as microstructures of the cement pastes via using humidity sensor, laser displacement measurer, MIP, TG/DSC, and SEM. Results indicated that, compared to the plain cement paste, incorporation of biochar provided efficient internal curing, maintaining a higher internal relative humidity and hence a reduced the autogenous shrinkage by 16.3% at the age of 180 h. An obvious synergetic effect on mitigating the autogenous shrinkage of cement paste was observed when the biochar was added with the combination of MEA in the cement paste. For instance, with the addition of 2 wt% biochar and 8 wt% MEA with a high reactivity (reactivity value of 45 s) gained an expansion of 80 microstrain rather than a shrinkage at the age of 180 h. Addition of biochar increased slightly the compressive strengths of the cement pastes at the late ages of 28d and 90d. This facilitates to offset partially the compromise on compressive strength of cement paste caused by the incorporation of MEAs alone. This study provides a novel and effective approach for mitigating the autogenous shrinkage of cement materials.

Effect of Nano-Materials on Autogenous Shrinkage Properties of Cement Based Materials

This paper presents an experimental investigation on the effect of nano-montmorillonite, carbon nanotubes, and nano calcium carbonate on autogenous shrinkage of cement based materials. Cement paste with different nano-montmorillonite dosage (1.0 wt.%, 2.0 wt.%, 3.0 wt.%), carbon nanotubes dosage (0.1 wt.%, 0.2 wt.%, 0.3 wt.%), and nano calcium carbonate dosage (1.0 wt.%, 2.0 wt.%, 3.0 wt.%) were compared with the reference group to assess the effects of nano-materials on cement paste. Results show that autogenous shrinkage of cement based materials containing nano-materials mainly occurs in the first 72 h. Nano-materials decrease the autogenous shrinkage of the investigated cement based materials at all ages. Compared with that of the reference group at the age of 168 h, the autogenous shrinkage of NM-modified cement based composites containing 3.0 wt.% NM decreased by as much as 57.4%; the autogenous shrinkage of CNTs-modified cement based composites containing 0.3 wt.% CNTs decreased by as much as 19.4%; the autogenous shrinkage of NC-modified cement based composites containing 2.0 wt.% NC decreased by as much as 17.1%. Electrochemical AC (Alternating Current) impedance spectroscopy results show that the resistance of the pore solution electrolyte of specimens containing nano-materials increases with age, and is less than that of specimens without nano-materials, which illustrates that the pore size of nano-modified cement based material is finer and autogenous shrinkage is smaller. Scanning electron microscope results show that the structure of cement matrix is denser with more hydration products by adding nano-materials. Nano-montmorillonite releases water to reduce self-drying effect during the process of hydration for its well water swelling. Carbon nanotubes have the nanometer filling effect and form a continuous network to restrain the early autogenous shrinkage of cement paste. Nano calcium carbonate not only decreases the porosity of the cement paste, but also reacts with tricalcium aluminate to generate the expanded product calcium carboaluminate for compensating autogenous shrinkage of cement paste.

Mechanisms behind radiation-induced deterioration of concrete

This paper describes the mechanism of radiation-induced deterioration of concrete and its components based on the literature review. The deterioration mechanism in different levels starting from the interaction between neutron and nucleus through the mineral metamictization and cement paste shrinkage up to the reduction of mechanical properties of concrete is explained in detail. All basic dependencies and patterns of volumetric change of minerals, aggregates, cement paste and finally concrete are also described in order to create a base for the future development of numerical models. Finally, the reduction of concrete mechanical properties is in correlation with its volumetric expansion. The radiation-induced volumetric expansion of concrete is affected by irradiation conditions (neutron fluence, neutron spectrum and temperature) and concrete composition (the amount, the proportion, the type and the structure of the minerals in the aggregate composition and the amount, the composition, the age and the structure of the cement paste).

Influence of concrete additives on cement paste shrinkage

The paper deals with the analysis of the effect of chosen latent hydraulic additives on concrete drying shrinkage. Variant dosage of latent hydraulic additives in cement paste was examined. Measuring of shrinkage in time was accompanied by testing of compressive strength and tensile strength at the age 28 days and 280 days. Results of investigations are summarized and compared.

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.

Effect of temperature rising inhibitor on autogenous shrinkage of cement pastes

This study examines autogenous shrinkage behavior of cement pastes affected by temperature rising inhibitor (TRI). Dynamic elastic modulus, hydration kinetics, mineral phase compositions, pore solution and microstructure development were investigated by ultrasonic method, isothermal calorimetry, quantitative X-ray diffraction, inductively coupled plasma-optical spectroscopy and electrical resistivity, respectively. The results of the investigation indicate that reduction in surface tension of the pore solution is not due to the impact of TRI. Conversely, it is shown that growth process of ettringite crystals in pore solution the inhibition is delayed which results from the decreased growth rate of ettringite in pore solution and the slow dissolution rate of aluminum from clinkers affected by TRI. This is used to explain the derivation trend of mineral phases of clinkers, chemical compositions of pore solution, and decreases in the autogenous shrinkage of cement pastes. Experiments involving TRI and pure calcium sulfate aluminum clinker indicate expansion stress generation for a longer period when compared to that in the cement pastes only containing TRI, thereby confirming delayed ettringite growth mechanism.

Effect of amorphous metallic fiber on mechanical properties of high-strength concrete exposed to high-temperature

This study experimentally examined the effect of amorphous metallic fiber on the mechanical properties of heated high-strength concrete with compressive strengths of 100 and 120 MPa. The mixing ratios of amorphous metallic fiber were 0.3 and 0.5 vol%. Polypropylene fiber was added at the ratios of 0.15 and 0.25 vol% according to the compressive strength of concrete. Specimens were prepared at six levels depending on the compressive strength of concrete and the mixing condition of the fiber. Specimens were heated up to the target temperatures of 100, 200, 300, 500, and 700 °C at the rate of 1 °C /min, and the respective compressive strength and elastic modulus were measured after 24 h cooling periods. The thermal expansion strain was experimentally measured while the specimen was heated (maximum temperature of 700 °C). The addition of amorphous metallic fiber can improve the degradation of compressive strength and elastic modulus of high-strength concrete (which was heated at temperatures above 300 °C). This effect could be confirmed by measurements of the thermal expansion and the peak strains. The addition of amorphous metallic fiber was effective in suppressing cracks that occurred owing to the expansion of aggregate and the shrinkage of cement paste.

Evaluation of Properties and Microstructure of Cement Paste Blended with Metakaolin Subjected to High Temperatures.

The effects of 10% metakaolin addition on compressive strength, water absorption, shrinkage and microstructure evolution of cement paste after elevated temperatures exposure from room temperature to 800 °C were evaluated. The experimental results show that compressive strength increases at 200 °C and 400 °C compared with that obtained at ambient temperature. Up to 800 °C, compressive strength decreases rapidly. The addition of 10% metakaolin leads to the enhancement of compressive strength regardless of exposure temperatures. After thermal exposure at 400 °C, compressive strength reaches the maximum value. Thermal exposure degrades pore structure. A polynomial equation was used to indicate the shrinkage of cement paste or metakaolin-blended cement paste with testing days. Mechanical properties, permeability resistance, and shrinkage in cement pastes are closely related to the microstructure development. 10% metakaolin addition presents better thermal resistance, lower shrinkage and denser microstructure compared with pure cement paste before and after thermal exposure.

Hydration, Strength, and Shrinkage of Cementitious Materials Mixed with Simulated Desalination Brine

Abstract The process of desalination results in the production of a hypersaline waste by-product known as reject brine. In some locations, this reject brine is dumped back into the ocean, which has potentially detrimental effects on water quality and marine life. This study was carried out to investigate whether this brine could potentially be used to manufacture cementitious materials. The effects of different concentrations of simulated reject brine on hydration kinetics, compressive strength, and drying shrinkage of cement paste and mortar were investigated. Cement paste and mortars were prepared using a water-to-cement ratio of 0.45 and were mixed with simulated reject brine, tap water, and diluted reject brine (an equal mass mixture of reject brine and tap water). The results show that the reject brine causes an acceleration of early cement hydration; however, this effect is negligible at later ages. Mixtures containing reject brine have higher compressive strength at early ages, although this difference is reduced at 91 d. The reject brine causes a drastic increase in the drying shrinkage. The difference between the results obtained using reject brine and diluted reject brine were generally insignificant, which suggests that the effects of solution composition on the observed properties were not strong when solution concentrations were greater than a threshold value. Although these results are preliminary and further feasibility studies, including research on concrete durability, are required, the results suggest that reject brine may be used to make unreinforced concrete or concrete reinforced with noncorrosive materials.

Drying and shrinkage of cement paste for 3D printable concrete

The article presents the results of the study of drying and shrinkage of three compositions of cement paste different in the content of microsilica and superplasticiser within the range of variation typical for 3D printable concrete compositions. Plate samples kept in the environment with RH = 20, 30, 50, 70 % were used to simulate different drying conditions of material in thin layers of 3D printing structures. Rates of mass loss and shrinkage of hardened cement paste are compared with criterial parameters of their structure. It is shown that increased dosage of microsilica and superplasticiser ensures the reduction of total volume of pores, increase of the content of nanopores, while simultaneously the area and energy activity of solid phase surface increases. These factors secure the ability of cement paste to better retain the water in the structure under all drying conditions. As a result, reduction of absolute values of mass loss by 3 - 4 times and shrinkage by 2 times in comparison with reference system is ensured for cement paste with maximally dense structure. At the same time, there is a twofold increase of relative deformability on each percent of mass loss, which may lead to significant tension in 3D printing structures due to moisture gradient.

Autogenous Shrinkage of Cement Paste Interpreted by Electrical Resistivity and Capillary Stress at Early Age

Abstract Autogenous shrinkage caused by the self-desiccation of cement-based materials at early age requires more attention from researchers because it can increase the risk of cracking in concrete. This article presents the relationships among autogenous shrinkage after final setting, the estimated effective capillary stress, and electrical resistivity of cement pastes. Autogenous shrinkage, internal relative humidity, chemical shrinkage, and electrical resistivity were measured for the plain cement paste that had water to cement ratios (W/C) of 0.3, 0.35, and 0.4 at early age. Electrical resistivity and its rate curve were presented to analyze the influence of W/C on the hydration process. A fitting function containing W/C, electrical resistivity, and three constant parameters was put forward to quantify the relationship between autogenous shrinkage and electrical resistivity. The autogenous shrinkage of cement paste at different ages can be predicted by the resistivity at 24 h; the relationship between electrical resistivity at 24 h and the effective capillary stress S·σcap at 24 h, 48 h, 72 h, and 96 h was also established to support the effectiveness of relating the self-desiccation development trend and electrical property of cement paste. This study introduces innovative and quick methods to estimate the autogenous shrinkage of cement paste by electrical resistivity.