Shrinkage Of Cement Paste Research Articles

Formulation and performance comparison of grouting materials for semi-flexible pavement

Semi-flexible pavement has been widely used for good performance, however, few studies have been made on effects of composition and formulation on grouting material. Therefore, this paper focuses on effects of composition and formulation on two typical grouting materials, including cement paste and cement mortar. The optimal formulations of these two materials are determined, and their performances are compared in terms of fluidity, strength and drying shrinkage. The result shows that fluidity, strength and drying shrinkage of cement paste and cement mortar vary with their composition, and both of the two materials can meet the technical requirements in the appropriate formulations. Comparatively, cement paste with its optimal formulation is more suitable as a grouting material for its better performance. The optimal ratio of water to cement is 0.58, the coal ash accounts for 10% and mineral powder accounts for 10%.

Influence of Nano-SiO2on the Consistency, Setting Time, Early-Age Strength, and Shrinkage of Composite Cement Pastes

The study outlined the raw materials and mix proportions to prepare composite cement pastes with the addition of silica-based micro- and nanoparticles. The effects of amorphous nano-SiO2on the early-age properties, including the consistency, setting time, early-age strength, and chemical and autogenous shrinkages, were investigated. Under the condition of the same dosage of superplasticizer used, the consistency of cement paste with nano-SiO2is higher than that with silica fume. Significant reductions of the initial and final setting times are observed especially for nano-SiO2addition groups, and the time difference between the initial and final setting times goes up with the increasing proportions of nano-SiO2. The addition of nano-SiO2is more helpful to the improvement of early-age strengths of the paste with or without fly ash admixed than silica fume additive for the same mass proportion. Both the chemical and autogenous shrinkages of cement paste develop with the increasing amount of micro- or nanolevel silica particles; however, nano-SiO2plays a more active role than silica fume in inspiring early-age shrinkage. The physical and chemical mechanisms of nano-SiO2in cement paste are also discussed.

Применение ультрацеллюлозного волокна для повышения прочности и усадки цементных растворов, подверженных нормальным и агрессивным условиям выдерживания

Применение ультрацеллюлозного волокна для повышения прочности и усадки цементных растворов, подверженных нормальным и агрессивным условиям выдерживания

Hysteresis from Multiscale Porosity: Modeling Water Sorption and Shrinkage in Cement Paste

The importance of concrete and cement to civil infrastructure cannot be overstated, yet there are still surprising gaps in our knowledge of these systems, which are unexpectedly complex. One basic example is that cement paste shrinks when water is removed from its multiscale pore network, and swells when water is added, but the mechanism is unclear. In a complete reassessment of this phenomenon, the authors differentiate the physical behavior of water in the layered nanostructures of cement hydrates from that in larger gel and capillary pores, linking microstructure to macroscopic material properties.

Relations among electrical resistivity, chemical and autogenous shrinkage of cement pastes

Electrical resistivity, chemical shrinkage and autogenous shrinkage were measured for cement pastes with different water to binder (w/b) ratios (0·30, 0·35 and 0·40) and fly ash replacements of cement (0%, 30% and 50%). The electrical resistivity, chemical shrinkage and autogenous shrinkage of the pastes decreased with increasing w/b ratio and fly ash content after final setting. The autogenous shrinkage development over time could be divided into a setting period, a rapid growth period, an expansion period and a slow growth period. Based on the test results, the chemical shrinkage and the autogenous shrinkage were linearly correlated to electrical resistivity after hydration for 24 h and 30 h respectively. The linear relationships will help to expand the application of electrical resistivity measurements. The parameter γ, defined as the proportion of autogenous shrinkage to linear chemical shrinkage after the final set, decreased with time due to increasing paste stiffness. This parameter will help researchers quantitatively understand the volume proportion of autogenous shrinkage and empty cavities during hydration.

Mechanism of Change in Splitting Tensile Strength of Concrete during Heating or Drying up to 90°C

Changes in temperature and relative humidity affect splitting tensile strength of concrete but the mechanisms are left unknown. This study aimed to clarify the mechanism through experiments using control mortar specimen and concrete specimens with two types of coarse aggregate of different shrinkage behavior mixed with the control mortar. Specimens were shaped in a thin plate for a faster equilibrium with the ambient drying conditions. Dying of different temperatures or relative humidities were maintained till the mass of specimens become constant. Then length changes, mass changes and splitting tensile strength were determined. It was shown that changes in strength of control mortar became more significant as drying conditions became severer while the change was not always monotonic. Compared with existing studies on shrinkage of cement pastes, the shrinkage of mortar specimens was supposed to be affected by the changes in strength of cement paste and by increase in strength as a result of multiple crack formation that occur due to fine aggregates. Changes in strength of concretes were affected by the change in mortar strength particularly at a relative humidity ranging from 0.80 to 0.43, where effects of fine cracks due to restraint of aggregate were imposed and strength reduction became more significant when coarse aggregate with a lower shrinkage was used. The restraining effect of coarse aggregate was confirmed also during heating higher than 40°C resulting in reduction of strength. It was concluded that the changes in strength of concrete during drying were mainly affected by both changes in mortar strength and restraint of coarse aggregate.

The Influence of Based on Polyalcohols Additive on the Cement Paste Shrinkage

The influence of a shrink-resistant “Estrifan Additive RCL” additives on the cement paste shrinkage was researched. The cement paste shrinkage is reduced when we use this additive. When the content of additives is more than 2 % there is expansion in the initial stage of hardening. The extension period is longer and the value of expansion deformation is higher, the additive dosage is higher. The presence of superplasticizer Muraplast FК48 enhances the initial expansion effect and shrinkage decrease by reducing the rate of evaporation of water. On the contrary, in a separate action superplasticizer increases the cement paste shrinkage.

Influence of superplasticizers on early age drying shrinkage of cement paste with the same consistency

The influence of superplasticizer (SP) on the early age drying shrinkage of cement paste with the same consistency was investigated. To conduct the test, which lasted for 72 hours, three paste mixtures were used for comparison. The 72 hours early age drying shrinkage staring from the initial setting time was measured by a clock gauge. The pore size distribution was measured by Mercury Intrusion Method. The surface tension of capillary simulation liquid and mass loss of paste were also measured. The experimental results showed that the addition of SP increased the early drying shrinkage greatly. The ratios of water evaporation and the total free water in mixtures added with SPs showed great differences. SPs fined the capillary pores of paste, and the volume of pore with diameter within 50 nm was well consistent with shrinkage rate. The addition of SPs did not raise the capillary liquid surface tension. It showed that with the volume of pore with diameter within 50 nm and the ratio of water evaporation and the total free water a tolerable shrinkage result of paste added with SP could be predicted, and the elastic modulus could have an influence on the early shrinkage. These results have never been proposed before.

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.

Improvement of autogenous shrinkage measurement for cement paste at very early age: Corrugated tube method using non-contact sensors

Test methods for the measurement of autogenous shrinkage of cement paste were reviewed, and it is found that few methods can precisely determine the autogenous shrinkage of cement paste at very early age. Therefore, the corrugated tube method was improved by using non-contact linear variable differential transformer (LVDT) sensor for measuring the autogenous shrinkage of cement paste at very early age. The experimental results show that the transformation ratio of the volume deformation to length change for the designed non-contact system can be as high as 0.97, which gives a significant improvement compared to that for the contact system (0.87). Compared to the contact system, the designed non-contact system also has an improved repeatability: the typical standard deviations reach about 50μm/m and 10μm/m before and after setting, respectively.

Influences of a composite addition on the strength of mortar and shrinkage of cement paste

The influences of a composite addition on the strength of mortar as well as the shrinkage of cement paste were investigated. Portland cement, fly ash and a composite addition were used in binary and ternary cementitious blends. The composite addition used in this research was composed of an ultrafine dust collected from iron-smelting furnaces and a small amount of alkali chemicals. The test results indicate that the use of fly ash and the composite addition in the ternary blends enhanced the strength noticeably, especially at early age. Incorporation of the addition resulted in an increase of autogenous shrinkage, but the total shrinkage at 90 days was close to the control specimen when the sealed curing period was longer than 7 days. The longer the specimen cured under sealed conditions, the smaller the total shrinkage produced. An abrupt increase of drying shrinkage was observed as soon as the specimen was demoulded, no matter how long the specimen was cured under sealed conditions.

Measurement of chemical shrinkage of cement paste: Comparison study of ASTM C 1608 and an improved method

Chemical shrinkage of cementitious materials has significant contribution to the early volume change of concrete, therefore, precise measurement of chemical shrinkage of cementitous materials is increasingly concerned. In the present study, measurement methods for chemical shrinkage were reviewed, especially for dilatometry method specified in ASTM C 1608. It was found that the precision and repeatability of ASTM C 1608 method were significantly influenced by the water to cement (w/c) ratio and the thickness of cement paste, which can be attributed to the generation of voids in the cement matrix and the restraint of formed particle skeleton structure, especially when low w/c ratio and/or high thickness of cement paste were used. By adding a magnetic stirring bar to prevent the formation of skeleton structure of cement paste, the chemical shrinkage measurement was simplified and presented superior precision and repeatability than ASTM C 1608 method, and the obtained results had better correlation with the calculated chemical shrinkage.

Temperature dependence of autogenous shrinkage of silica fume cement pastes with a very low water–binder ratio

Ultra-high-strength concrete with a large unit cement content undergoes considerable temperature increase inside members due to hydration heat, leading to a higher risk of internal cracking. Hence, the temperature dependence of autogenous shrinkage of cement pastes made with silica fume premixed cement with a water–binder ratio of 0.15 was studied extensively. Development of autogenous shrinkage showed different behaviors before and after the inflection point, and dependence on the temperature after mixing and subsequent temperature histories. The difference in autogenous shrinkage behavior poses problems for winter construction because autogenous shrinkage may increase with decrease in temperature after mixing before the inflection point and with increase in temperature inside concrete members with large cross sections.

Shrinkage of Blended Cement Pastes with Mineral Additions

Mineral additions such as fly ash and silica fume are industrial by products, and play an important role in properties improvement for construction materials. In this work, the shrinkage of cement paste blended with fly ash and silica fume by different substitute ratio was studied. Pore structures of specimens at different ages were determined by mercury intrusion porosimetry (MIP) and shrinkage deformation was measured by standard shrinkage tests. The effects of mineral addtions on shrinkage were discussed. The results show that the fly ash was significantly effective on shrinkage at early ages. Based on the research, several suitable advices were offered to optimize the performances of materials and reduce the shrinkage.

Relationship between Internal Relative Humidity and Autogenous Shrinkage of Cement Paste with Supplementary Cementitious Materials (SCM)

The influence of water to binder (W/B), types and dosage of supplementary cementitious materials (SCM) on the internal relative humidity (IRH) and autogenous shrinkage (AS) of cement pastes caused by self-desiccation were investigated, and their relationship was discussed. The results show that, W/B is a main factor that affects IRH change and AS of cement pastes with SCM. With the decrease of W/B, IRH of cement pastes decreases, but AS of cement pastes increases. Different types and dosages of SCM affect the IRH differently; fly ash (FA) reduces AS, silica fume (SF) increases AS, and the effect of GBFS on AS is between FA and GBFS. The linear correlation between the change of IRH and AS of cement pastes with SCM is established.

Surface modification of fly ashes with carbide slag and its effect on compressive strength and autogenous shrinkage of blended cement pastes

Surfaces of grade III fly ashes were modified through mixing with carbide slag and calcining at 850 °C for 1 h. Mineralogical compositions and surface morphology of fly ashes before and after modification were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Effect of surface-modified fly ashes on compressive strength and autogenous shrinkage of blended cement pastes was investigated. Microstructures of cement pastes were examined by backscattered electron (BSE) imaging and mercury intrusion porosimetry (MIP). The experimental results showed that β-C2S was formed on the surfaces of fly ashes after modification. Hydration of β-C2S on the surface-modified fly ashes densified interface zone and enhanced bond strength between particles of fly ashes and hydrated clinkers. In addition, surface modification of fly ashes tended to decrease total porosity and 10–50 nm pores of cement pastes. Surface modification of fly ashes increased compressive strength and reduced autogenous shrinkage of cement pastes.

Effect of Nano-CaCO3 on Properties of Cement Paste

In this paper, effect of nano-CaCO3 (NC) on properties of cement paste was studied. Experimental results showed that NC had no effect on water requirement of normal consistency of cement. However, with the increase of NC content, the flowability decreased and the setting time of fresh cement paste was shortened. The early hydration of cement was activated by NC. The strength and the early age shrinkage of cement paste were also studied. Mechanical experiments indicated that the flexural and compressive strength of hardened cement paste increased with the addition of NC at the age of 7d and 28d, and the optimal content of NC was 1%. The early age (12h) shrinkage of cement paste containing 1% NC was the most prominent which could decrease the shrinkage strain obviously.

Influence of Thermomechanical Pulp Fiber Compositions on Internal Curing of Cementitious Materials

AbstractThis research examines the efficiency of thermomechanical pulp (TMP) fibers, both untreated and after chemical treatment to produce holocellulose and α-cellulose, for internal curing. In addition, the effect of TMP fibers on early hydration behavior was investigated. The results show that TMP and α-cellulose fibers had a negligible effect on cement hydration. Holocellulose, conversely, significantly reduced the rate of hydration, noticeably delaying setting time. The addition of the fibers in dosages to provide an additional amount of entrained water of 0.05 g per gram of cement resulted in a decrease of early autogenous shrinkage of cement paste. Holocellulose, reducing autogenous shrinkage of cement paste by 93%, was shown to be the most effective for internal curing; however, its adverse effect on cement hydration may require acceleratory admixtures when used in concrete. Thermomechanical pulp and α-cellulose showed a similar efficiency in mitigating autogenous shrinkage; these fibers reduced s...

Effects of MgO-based expansive additive on compensating the shrinkage of cement paste under non-wet curing conditions

Abstract Expansive additives are widely used to compensate the drying shrinkage of cement-based materials to avoid cracking. However, the expansion of conventional ettringite-bearing expansive additive depends strongly on wet curing and is mainly generated at early age, and hence it may not work well in concretes without sufficient water supply or exhibit long-term shrinkage. MgO-based expansive additive, for which less water is needed for the formation of Mg(OH) 2 in comparison to ettringite, was prepared and its compensating effect on the autogenous shrinkage and late age thermal shrinkage of Portland and fly ash cement pastes at low water-to-cement ratio was investigated. The tests were conducted under sealed condition, so that the moisture exchange with the environment was prevented. Results show that, even under the non-wet curing condition, the shrinkages of cement pastes can be compensated effectively. Microstructure analysis by scanning electron microscope indicates that the macro-expansion of cement pastes is probably caused by the locally restrained expansion of MEA due to the hydration of MgO.

Research on Shrinkage and Cracking of Cement Paste Based on Environmental Scanning Electron Microscope

In order to study the shrinkage characteristics of cement paste, environmental scanning electron microscope was used to observe the microstructure shrinkage of cement paste and cement mortar under different humidity. The results showed that : with the relative humidity decreased from 80% to 10%, the shrinkage cracking of paste microstructure appeared in different degree and increased continuously,also the regression analysis showed the relative humidity and shrinkage was conical relationship.