Shrinkage Of Cement-based Materials Research Articles

Role of casting and curing conditions on the strength and drying shrinkage of greener concrete

The shrinkage of cement-based materials is a critical dimensional property that needs proper attention as it can influence the corresponding characteristics especially when the preparation of such cement-based material is done in hot weather. Studies have shown that the casting or curing conditions influence the performance of concrete. However, there is limited understanding of the combined role of casting temperature and curing conditions, especially for concrete made with unconventional binders. In this study, five supplementary cementitious materials (SCMs) were utilized as the substitute of the ordinary Portland cement (OPC) at different ratios to produce greener concrete and improve its characteristics and sustainability. The influence of four casting temperatures (i.e., 25°C, 32°C, 38°C, and 45°C) and two curing regimes (i.e., covering of samples using wet burlap and applying curing compound on the surface of samples) on the corresponding compressive strength and drying shrinkage at various ages was studied. The outcomes of this research revealed that the composition of the binders has a substantial impact on the characteristics of concrete. In addition, the casting temperature and curing regimes also have a huge role on the compressive strength of concrete produced with binary binders. For example, the compressive strength at 3days of concrete made at 25°C made with binary binders was reduced up to 31% compared to that made with only OPC as the binder when cured using wet burlap. Nonetheless, less than 38 ℃ was suitable to minimize the durability issues in the studied blended cement mixes.

Mitigating autogenous shrinkage using a combination of superabsorbent polymer and magnesia-based expansive additive

Various strategies have been developed to mitigate the autogenous shrinkage of cement-based materials (CBMs), including internal curing and shrinkage compensation. However, the sole use of internal curing or shrinkage compensation is insufficient in many cases. In this study, magnesia-based expansive additives (MEAs) coupled with a superabsorbent polymer (SAP) were investigated as internal curing agents to mitigate the autogenous shrinkage of cement pastes. The internal relative humidity (RH), autogenous deformation and compressive strength of cement pastes containing two different types of MEAs and SAP were examined. The results showed that, with the incorporation of SAP, the RH in the cement paste was maintained at a higher level than that in cement pastes without SAP, and hence autogenous shrinkage was reduced. The combination of SAP and MEA provided very effective compensation for the autogenous shrinkage of cement paste. Moreover, the cement paste containing 8 wt% MEA and 0.2 wt% SAP produced a gentle expansion of 111 microstrain rather than shrinkage. This was attributed to the increased hydration degree of magnesia owing to the additional water supply provided by the SAP. This study provides a novel and efficient way to mitigate the autogenous shrinkage of CBMs.

Reinforcing Mechanisms of Coir Fibers in Light-Weight Aggregate Concrete.

Due to the requirement for developing more sustainable constructions, natural fibers from agricultural wastes, such as coir fibers, have been increasingly used as an alternative in concrete composites. However, the influence of coir fibers on the hydration and shrinkage of cement-based materials is not clear. In addition, limited information about the reinforcing mechanisms of coir fibers in concrete can be found. The goal of this research is to investigate the effects of coir fibers on the hydration reaction, microstructure, shrinkages, and mechanical properties of cement-based light-weight aggregate concrete (LWAC). Treatments on coir fibers, namely Ca(OH)2 and nano-silica impregnation, are applied to further improve LWAC. Results show that leachates from fibers acting as a delayed accelerator promote cement hydration, and entrained water by fibers facilitates cement hydration during the whole process. The drying shrinkage of LWAC is increased by adding fibers, while the autogenous shrinkage decreases. The strength and toughness of LWAC are enhanced with fibers. Finally, three reinforcement mechanisms of coir fibers in cement composites are discussed.

Simplified chemo-mechanical model of hydration/expansion of calcium-oxide-type expansive agent in cement-based materials

The restrained volume expansion of expansive agents during hydration is often used to offset strains caused by the shrinkage of cement-based materials (CBMs). The hydration and expansion process of a laboratory-prepared calcium-oxide (CaO)-type expansive agent (CEA) in CBMs and modelling of the same are discussed in this paper. Based on isothermal calorimetry and thermogravimetry/differential thermal analysis, the hydration behaviour of the CEA in cement paste was examined, based on which the hydration kinetics were analysed and the apparent hydration activation energy of the CEA was calculated. Based on the degree of hydration, a chemo-mechanical model of the expansion of the CEA in CBMs was developed and analysed by comparison with experimental data obtained by the dual-ring restraint test method. Based on this model, it is possible to predict the expansion performance and crack resistance of concrete containing CEA agent.

Effects of the hydration reactivity of ultrafine magnesium oxide on cement-based materials

The size of magnesium oxide may greatly affect its behaviour in cement-based materials (CBMs), and this has not been fully investigated. The reactivity of ultrafine magnesium oxide (UFM) of size 40 nm to 20 μm was assessed, and its effects on the compressive strength and volume stability of cement mortar were investigated. The results showed that the hydration of UFM followed the first-order reaction mode in the first 3 d and then slowed down due to the alteration of the reaction to the diffusion-controlled mode. UFM contributed to an increase in compressive strength and a decrease in shrinkage of CBMs at the very early age, but hindered the hydration of cement at later ages, coarsened the microstructure, and decreased the later-age shrinkage to a much smaller extent than normal light-burnt magnesium oxide. The relatively high hydration reactivity of UFM may contribute to the formation of a more compact gel structure around cement particles at the very early age, which may hinder the reaction of cement at later ages, thus leading to the slowed property gain of CBMs at later ages. The findings from this study may help in the selection of magnesium oxide types for achieving a desired CBM with certain properties.

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.

An Automated Monitoring System to Measure Shrinkage of Cement-Based Materials in Multiple Environments

Abstract An automated monitoring system was developed for the measurement of shrinkage of cement-based materials. This system combines continuous dynamic measurements conducted on multi-group samples, the use of non-contact measurements and environment simulation technology. An automated data analysis method was developed and used to obtain shrinkage values. Furthermore, a correction method is proposed in an effort to calibrate these measurements. The early-age and long-term shrinkage behavior of multi-group samples were investigated by the use of this system under specific testing environments. This was done in an effort to understand the influence of climatic variations on shrinkage deformation properties. These experimental data can be used in numerical models to estimate shrinkage of similar specimens.

The Early-Age Drying Shrinkage of Cement-Based Materials with the same Workability after Temperature Compensation

The early age drying shrinkage of cement-based materials with same the same workability staring from the initial setting time was studied. Superplasticizers (SP) were used to get the same workability. The drying shrinkage of paste was measured by clock gauge, and CABR-NES deformation instrument was used to measure the shrinkage of concrete. Temperature probes were buried into both paste and concrete specimen cores to measure the temperature curve, and temperature deformation was considered into the early shrinkage. Results show the addition of SP increases much more shrinkage than the control group, and polycarboxylate SP increases more shrinkage than naphthalene SP. The different temperature peak time of different mixtures show that the addition of SP changes the hydration process of cement, and the shrinkage of cement-based materials after temperature compensation is bigger than the measured value in the first 6 hours, but the gap is not big.

Influence and Mechanism of Polymer Coating on Shrinkage of Cement-Based Materials

The influence of polymer coating on the shrinkage of cement-based materials is comparatively analyzed in this paper. First of all, the relationship between cement-based materials shrinkage and water loss is discussed. Furthermore, some surface topography differences and pore structure changes of cement-based materials causing by polymer coating are investigated. At last, the affecting mechanism of polymer coating on reducing cement-based materials shrinkage is investigated. The results show that polymer coating can significantly reduce the shrinkage of cement-based materials. A more thick coating gets a higher shrinkage reducing ratio. There is a close relationship between cement-based materials water loss ratio and shrinkage ratio. Polymer coating can make the micro-crack on cement-based materials surface disappear. The cement-based materials coated with polymer have a lower surface layer cumulative average porosity than blank control group. The evaporation of capillary water and the development of negative capillary pressure in cement-based materials are controlled by polymer coating, thus the shrinkage becomes small.

The equivalent pore pressure and the swelling and shrinkage of cement-based materials

The equivalent pore pressure and the swelling and shrinkage of cement-based materials

Drying, moisture distribution, and shrinkage of cement-based materials

The aim of this study was to develop a new method to determine hygral diffusion, film, and shrinkage coefficients of cement-based materials. These coeffcients are required for the numerical simulation of shrinkage strain and total deformation of concrete elements and structures using the finite element method. Both an experimental approach to determine the time-dependent relative humidity in the pore system of concrete and a numerical method to determine material coefficients on the basis of experimental data are described in this paper. The hygral diffusion coefficient can be expressed as function of moisture content and as function of relative humidity. An experiment is carried out with sliced specimens measuring 150×100×3 mm. Each specimen is prepared by piling up 11 slices and sealing the outer surfaces with aluminum sheet. The distribution of relative humidity is estimated by measuring the shrinkage strain on each slice at arbitrary drying times. An inverse analysis is then used to obtain the diffusion coefficient from the measured relative humidity distribution. A numerical approach based on the weighted residual method and on a nonlinear least squares method is proposed on the basis of the experimental results.

Drying, moisture distribution, and shrinkage of cement-based materials

Drying, moisture distribution, and shrinkage of cement-based materials

MOISTURE DISTRIBUTION, DIFFUSION COEFFICIENT AND SHRINKAGE OF CEMENT-BASED MATERIALS

MOISTURE DISTRIBUTION, DIFFUSION COEFFICIENT AND SHRINKAGE OF CEMENT-BASED MATERIALS