Development Of Autogenous Shrinkage Research Articles

Research Progress in the Application of Calcium-based Expansive Agents as Compensation for Autogenous Shrinkage in High-strength Concrete

In this study, comprehensive investigation of the shrinkage compensation mechanisms of calcium-based expansive agents (CEAs), their effects on the properties of (ultra) high-strength concrete (HSC/UHSC), and the existing problems in applying this methodology was conducted. Analyses showed that the rational use of CEAs under certain conditions could greatly or completely inhibit the development of autogenous shrinkage of HSC/UHSC, and significantly reduce the risk of associated cracking. However, it was found that the hydration of the CEAs affected the hydration process of other binders, thereby altering the microstructure of concrete. This was in turn observed to lead to a degree of decrease in compressive strength, flexure strength and elastic modulus, and the decrease rate increasing as with the rise in proportion of CEAs. Moreover, when attempting to improve the shrinkage compensation effects, increasing the amount of CEA presented a risk of delayed expansion cracking of HSC/UHSC. Neither the expansion mechanism, expansion conditions, nor the inhibition methods have yet been fully clarified in the current stage. Lastly, newly proposed Ca-Mg composite EAs were outlined, and the research prospects of Ca-Mg composite EAs in HSC/UHSC were explored.

Mechanical Properties of Ultra-High Performance Concrete (UHPC) and Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) with Recycled Sand

Use of high-cost raw materials such as quartz sand can limit wider application of ultra-high performance concrete in concrete construction. In this experimental study, recycled sand was used to fabricate ultra-high performance concrete (UHPC) and ultra-high performance fiber-reinforced concrete (UHPFRC). Green UHPC with ordinary Portland cement and industrial by-products such as silica fume, fly ash, as well as recycled sand was first developed through two-step packing density tests to optimize the mix design. UHPFRC was then developed based on the UHPC mix designs and by using 1%, 2%, or 3% 13-mm straight steel fibers (SSF). The compressive strength, elastic modulus, and flexural tensile strength was 128 MPa, 46.9 GPa, and 11.9 MPa, respectively, after 28 days at water-to-binder ratio of 0.17 and with 2% SSFs. All high-performance concretes in this work utilized 100% commercially available recycled sand that was produced by wet processing method. Mechanical characteristics such as strength, elastic modulus, and density, absorption, and voids of the UHPC/UHPFRC were investigated. Development of autogenous shrinkage of UHPC/UHPFRC with recycled sand was monitored for 12 weeks, while mercury intrusion porosimetry test and scanning electron microscopy were performed for microstructural investigation. Finally, the environmental impacts and economical aspects of the green UHPC were evaluated by life cycle assessment (LCA) and cost analysis.

Analysis of the development of autogenous shrinkage of CEM I 42.5R and CEM III/A 42.5N cement pastes with different water to cement ratios

In concrete technology, cements with a high content of Portland clinker are increasingly being replaced by blended binders with a lower carbon footprint. Such binders include blastfurnace cements, which are successfully used in concretes designed for large-scale elements, self-compacting concretes, as well as for the precast concrete industry. Blast furnace cements exhibit lower strength gain relative to Portland cements and a lower heat of hydration. Composites that incorporate them are significantly more resistant to the occurrence of thermal stresses at the early stages of curing of concrete. This paper provides a comparative study of the development of autogenous shrinkage of cement pastes made from CEM I 42.5R and CEM III/A 42.5N with a variable w/c ratio using the dilatometric method on a proprietary instrument covered by the patent PL241667. Furthermore, tests on consistency, setting times and compressive strength were performed after 2, 7 and 28 days of curing. From the analyses carried out, it was found that cement pastes containing blast furnace cement show greater autogenous shrinkage over a period of 28 days compared to pastes containing Portland cement. The pozzolanic reaction of granulated blast furnace slag contributes to the increase in recorded autogenous shrinkage. An increase in the water-cement ratio has an impact on the decreased strength gain, and the value of autogenous shrinkage. The research results indicate the need to take autogenous shrinkage into account when designing high-performance concretes containing blast furnace cement due to the increased susceptibility to shrinkage microcracks and for the durability of the material.

Effect of pretreated cow dung fiber on mechanical and shrinkage properties of cementitious composites

The proper disposal of cow dung waste has always been a great challenge for the agricultural sector in China and around the world. In this work, the cow dung was processed into a cheap renewable cow dung fiber (CDF) and applied into cementitious composites. The physicochemical properties of raw and alkali pretreated CDF were analyzed by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, single fiber tensile test and scanning electron microscopy. The strength and autogenous shrinkage of cementitious composites reinforced with the CDF were measured. The results showed that alkali pretreatment dissolved the amorphous components (i.e., hemicellulose and lignin) and enhanced the crystallinity of cellulose. The pretreatment of CDF by 1 mol/L NaOH solution led the 3 d′s compressive and splitting tensile strength of the CDF reinforced cementitious composites to increase by 21.8% and 12.5%, respectively. The presence of CDF, with or without pretreatment enabled to inhibit the development of autogenous shrinkage of cementitious paste. This work is expected to promote an alternative application for the recycling of cow dung waste in sustainable building materials.

Effect of n-C-S-H-PCE and slag powder on the autogenous shrinkage of high-strength steam-free pipe pile concrete

This study investigates the effect of the calcium silicate hydrate–Polycarboxylate ether nanocomposite (n-C-S-H-PCE) on the development of autogenous shrinkage and other relevant properties, including strength, hydration degree, elastic modulus, and capillary pressure. To measure the autogenous shrinkage development of concrete, a strain-temperature-humidity integrated acquisition system was used to continuously monitor the interior strain, temperature, and humidity evolutions of the concrete. The results show that the n-C-S-H-PCE has a pronounced enhancement effect on the mechanical properties up to 7 d. The early strength enhancement of the n-C-S-H-PCE can reach 64% at 1 d. Due to the fast hydration, the autogenous shrinkage is higher in the concrete containing n-C-S-H-PCE. And the slag powder also increases the autogenous shrinkage. Moreover, a model suitable for predicting the autogenous shrinkage of high-strength concrete, such as PHC pipe piles, is established. The prediction values are in good agreement with the experimental values. We finally conclude that the n-C-S-H-PCE increases the hydration degree, which results in a lower internal RH and a higher capillary pressure at the early hydration period compared with the reference concrete. This study provides a reference for the application of n-C-S-H-PCE and slag powder in concrete and the further prediction of the autogenous shrinkage for concrete containing those ingredients.

Effects of triethanolamine on autogenous shrinkage and drying shrinkage of cement mortar

Impacts of triethanolamine (TEA) on autogenous shrinkage, drying shrinkage and strength development of cement mortars were investigated. Hydration kinetics, pore structure and microstructure of hardened cement pastes (hcps) incorporated with TEA were systematically analyzed to reveal the working mechanism of TEA. Results show that TEA at dosages of 0.05%, 0.10% and 0.50% by weight of cement increases the autogenous shrinkage of cement mortars at 7d, which is mainly resulted from the promoting effect of TEA on the secondary hydration of aluminate phases (C3A and C4AF) and inhibiting effect on the hydration of the silicate phase (C3S) especially at 0.50% dosage. The morphology change of CH in the presence of TEA may also accelerate the development of autogenous shrinkage. In addition, TEA has no obvious effect on the drying shrinkage of cement mortars due to the similar moisture diffusion trends of cement mortars with and without TEA from 7d to 56d. Moreover, 0.05% and 0.10% TEA enhance the early strength of cement mortars while 0.50% TEA leads to an opposite effect. However, 0.05%, 0.10% and 0.50% TEA reduce the late strength at 28d and 56d. Pore structures are not responsible for the strength reduction, as indicated from the MIP and DVS results. Therefore, it is believed that strength reduction may be resulted from the incorporation of CH microcrystals into C-S-H structures.

Resistivity Measurements to Study the Early Chemical and Autogenous Shrinkage of a Binary Alkali-activated Slag-metakaolin System

Alkali-activated slag-metakaolin (AASM) has a lower shrinkage than alkali-activated slag, but its complex shrinkage behaviour remains elusive. In this paper, resistivity measurements were used to monitor the early chemical shrinkage and autogenous shrinkage evolution of AASM (containing 10%, 30%, 50%, or 70% metakaolin). The MK content greatly affected the development of autogenous shrinkage of AASM, and the specimens with 50% MK showed the lowest autogenous shrinkage of 49%. The presence of MK delayed the formation of calcium aluminosilicate hydrate (C-A-S-H) gels (the activation products of slag), thus mitigating autogenous shrinkage. A functional relationship between early autogenous shrinkage and resistivity was established, which showed that resistivity can be used to evaluate and predict the early autogenous shrinkage of AASM.

Autogenous deformation and coefficient of thermal expansion of early-age concrete: Initial outcomes of a study using a newly-developed Temperature Stress Testing Machine

Thermal and autogenous deformations of high-performance concrete at early ages have significant impact on the performance, serviceability, and durability of concrete structures. While substantial past research has significantly improved our fundamental understanding of the autogenous shrinkage and of the coefficient of thermal expansion (CTE) of cement paste and mortar, such understanding for concrete, especially modern types of high-performance concrete at early ages, remains inadequate. Accordingly, a new Temperature Stress Testing Machine (TSTM) capable of generating reliable data on autogenous shrinkage and CTE of concrete from very early ages has been built. After a review of relevant major aspects, key features of the newly-built TSTM are reported, with a focus on advanced thermal regulation and deformation capturing systems. The outcomes of a study using the newly-developed TSTM on autogenous deformation and CTE of early-age concrete (two mixtures with water-to-binder ratio of 0.35 and 0.42) subject to different curing temperatures (23, 35 and 45 °C) are then presented. Higher curing temperatures significantly accelerate the development of autogenous shrinkage at very early ages, whereas after the initial period, the magnitude of autogenous shrinkage cured at the intermediate temperature of 35 °C gradually becomes the largest. Despite this cross-over, the maturity concept appears appropriate to approximate the effect of curing temperature on autogenous shrinkage of concrete at early ages. The linear CTE of early-age concrete, obtained using stepped temperature profiles, follows a clear rising trend after setting. Based on the newly-measured CTE, an attempt was made to separate thermal strain and self-desiccation shrinkage, in which the presence of non-negligible delayed thermal strain became evident.

The Influence of Superabsorbent Polymers and Nanosilica on the Hydration Process and Microstructure of Cementitious Mixtures

Superabsorbent polymers (SAPs) are known to mitigate the development of autogenous shrinkage in cementitious mixtures with a low water-to-cement ratio. Moreover, the addition of SAPs promotes the self-healing ability of cracks. A drawback of using SAPs lies in the formation of macropores when the polymers release their absorbed water, leading to a reduction of the mechanical properties. Therefore, a supplementary material was introduced together with SAPs, being nanosilica, in order to obtain an identical compressive strength with respect to the reference material without additives. The exact cause of the similar compressive behaviour lies in the modification of the hydration process and subsequent microstructural development by both SAPs and nanosilica. Within the present study, the effect of SAPs and nanosilica on the hydration progress and the hardened properties is assessed. By means of isothermal calorimetry, the hydration kinetics were monitored. Subsequently, the quantity of hydration products formed was determined by thermogravimetric analysis and scanning electron microscopy, revealing an increased amount of hydrates for both SAP and nanosilica blends. An assessment of the pore size distribution was made using mercury intrusion porosimetry and demonstrated the increased porosity for SAP mixtures. A correlation between microstructure and the compressive strength displayed its influence on the mechanical behaviour.

Prediction model for internal relative humidity in early-age concrete under different curing humidity conditions

The decrease of internal relative humidity (IRH) in early-age high performance concrete (HPC) may increase the autogenous shrinkage under the combined effects of self-desiccation and moisture diffusion. Correspondingly, the tensile stress induced by restrained shrinkage may cause premature cracking of HPC. Evaluating the cracking potential of concrete needs to know the development of autogenous shrinkage. The prediction of autogenous shrinkage requires quantitative analysis of the variations of IRH in HPC. Although the variations of IRH and prediction models for IRH in concrete have been studied, a prediction model for the IRH in HPC at early age based on experimental results considering the effect of curing humidity remains lacking. Thus, the critical time of IRH, IRH, IRH decrease rate, and the moisture diffusion coefficient of HPC under different curing humidity conditions were studied in this research. Experimental results and corresponding analysis demonstrated that: (1) the critical time of IRH in sealed HPC was longer than that in unsealed HPC under different curing humidity conditions, and the critical time of IRH in unsealed HPC increased as the curing humidity increased; (2) the IRH in unsealed HPC increased as the curing humidity increased at the same curing age; (3) the IRH decrease rate of sealed or unsealed HPC gradually decreased with the growth of age, and the IRH decrease rate of unsealed HPC decreased as the curing humidity increased at the same curing age; (4) the moisture diffusion coefficient of unsealed HPC was calculated, and the prediction model for IRH in HPC at early age under the combined effects of self-desiccation and moisture diffusion considering the effect of curing humidity was proposed.

A mechanistic model for the time-dependent autogenous shrinkage of high performance concrete

An accurate prediction of time-dependent autogenous shrinkage behaviors of concrete, especially for high performance concrete (HPC) at an early age, is of great significance to assess and control the cracking risks of restrained structural elements. In this study, based on the capillary tension theory, a mechanistic model for evaluating the time-dependent autogenous shrinkage behaviors of high performance concrete is proposed. A total of 416 data points including the concrete composition, curing condition, age of concrete, water-to-cement (binder) ratio, internal relative humidity, elastic modulus, and measured autogenous shrinkage are selectively collected for the model establishment. The effects of silica fume on the development of autogenous shrinkage are also considered. Upon the sound physical basis, the model requires only a few parameter inputs related to the mixture proportion and physicochemical properties of constituents. The reasonable agreements between the analytical predictions and independent experimental results, as well as common used formulas from different codes (i.e., ACI 209, Eurocode 2, and Model Code 2010), demonstrate that the time-dependent evolution of autogenous shrinkage of HPC can be reasonably predicted by the model proposed in this study.

Tensile response of low clinker UHPFRC subjected to fully restrained shrinkage

This paper addresses the tensile response of Strain Hardening Ultra High Performance Fiber Reinforced Concretes (SH-UHPFRC) subjected to restrained autogenous shrinkage deformations under full and partial restraint conditions, right after casting and until one month. The development of autogenous shrinkage and corresponding eigenstresses under various degrees of restraint were studied for two types of mixes; Mix I with type I cement and silica fume, and Mix II with silica fume and 50% mass replacement of type I cement with limestone filler. The tests under 100% restraint conditions are the first of their kind on SH-UHPFRC and the results show that under these conditions, the material enters into the strain-hardening domain of the tensile response. The development of eigenstresses was much slower in the Mix II when compared to that of Mix I. The development of the dynamic elastic modulus and heat of hydration were also studied and put into perspective.

Mechanisms of autogenous shrinkage of alkali-activated fly ash-slag pastes cured at ambient temperature within 24 h

This paper aims to provide a better understanding of autogenous shrinkage of alkali-activated fly ash-slag (AAFS) pastes at very early age (<24 h). The autogenous shrinkage of AAFS pastes with 10%, 20% and 30% slag replacement ratios of fly ash is measured. The results show that increasing the slag content in AAFS pastes would accelerate the chemical reaction process and cause a higher autogenous shrinkage and chemical shrinkage. The autogenous shrinkage of AAFS pastes in the liquid stage (from 0 h to initial setting time) is caused by chemical shrinkage, which arises from the absolute volume reduction of reaction products comparing with the original volume of unreacted binder. This phenomenon is similar to that found in Portland cement (PC) systems. Nevertheless, in hardening stage (from final setting time to 24 h) the autogenous shrinkage may be not fully attributed to the self-desiccation process that occurs in PC systems. Some other reactions including the continuous reorganization and rearrangement of aluminosilicate gel structure may also contribute to the development of autogenous shrinkage. In addition, the autogenous shrinkage in early 24 h occurs mainly due to volume contraction by chemical shrinkage in fresh state, which occupies approximately 70% of total autogenous shrinkage.

Effects of mix proportion and curing condition on shrinkage behavior of HPFRCCs with silica fume and blast furnace slag

This study investigated the effects of mixture proportion and curing condition on the mechanical and shrinkage behaviors of high-performance fiber-reinforced cementitious composites (HPFRCCs). Different water-to-binder (W/B) ratios and amounts of mineral admixtures, such as zirconium silica fume (Zr SF) and blast furnace slag were evaluated. The test results indicate that initial steam-heat curing accelerated the strength development and was sufficient to develop its full strength. The ultimate autogenous shrinkage was insignificantly affected by the curing conditions, but the heat curing accelerated the development of autogenous shrinkage. HPFRCC with a lower W/B ratio and greater amount of Zr SF exhibited higher autogenous shrinkage but lower drying shrinkage. In addition, the amount of total shrinkage of HPFRCC was more effectively reduced by providing heat curing when a higher W/B ratio and a smaller amount of Zr SF were used. There were no increases in the autogenous and drying shrinkage for HPFRCC immediately after finishing the initial heat curing, meaning that there is no possibility of shrinkage cracks forming in HPFRCC elements after the heat curing process. Finally, the autogenous shrinkage behaviors of HPFRCC were simulated with several prediction models from literature and an optimized model, considering equivalent age, was suggested.

Efficiency of internal curing by superabsorbent polymers (SAP) in PC-GGBS mortars

This paper evaluates the effect of superabsorbent polymers (SAP) on hydration and microstructure of PC-GGBS mortars. Development of autogenous shrinkage, microstructural characteristics (MIP/SEM) and compressive strength were analysed during the first 90 days. Four levels of Portland cement (PC) replacement by GGBS (0%, 25%, 50% and 75%) and two types of SAP with different water absorption capacities were considered. The results proved the efficiency of internal curing by SAPs in PC-GGBS systems due to significant reduction in autogenous shrinkage, especially for higher contents of GGBS. SAP facilitates GGBS hydration activated by portlandite; its products can be deposited into the nano pores leading to a small relative expansion of the hardened bulk volume. This process is initiated during the second week and it lasts until the sixth week. Despite increased total porosity, compressive strength of SAPs modified mortars is comparable to the reference samples for low GGBS contents in advanced ages.

Influence of the w/c ratio and aggregate composition on the autogenous shrinkage in self-consolidating concrete

Paper presents the analysis of shrinkage development in selfconsolidating concretes (SCC). Concretes were cured for 28 day in an insulated environment. The shrinkage was tested on 35x150x1150 mm samples. The specimen had the same volume as ring specimen proposed in the ASTM method of testing the susceptibility of concretes to cracking caused by the restricted radial shrinkage. Linear deformation of concrete samples was measured in constant periods of 500 s using dial gauges with digital data loggers. Conducted tests showed the influence of w/c ratio of 0.28, 0.34, 0.42 and aggregate composition on the development of the autogenous shrinkage in self-consolidating concretes. Additionally, rheological properties of the concrete mixes were tested and compressive and splitting strength was determined. Conducted research allowed to evaluate the influence of w/c ratio and natural aggregate composition on the development of autogenous shrinkage in different stages of curing of SCC.

Experimental Study on Autogenous and Drying Shrinkage of Steel Fiber Reinforced Lightweight-Aggregate Concrete

Steel fiber reinforced lightweight-aggregate concrete (SFRLAC) has many advantages applied in structural engineering. In this paper, the autogenous shrinkage and drying shrinkage of SFRLAC for up to 270 days were measured, considering the effects of types of coarse and fine aggregates with the changes of water-to-binder ratio and volume fraction of steel fiber, respectively. The properties of mix workability, apparent density, and compressive strength of SFRLAC were also reported and discussed in relation to above factors. Test results show that the development of autogenous and drying shrinkage of SFRLAC was fast within 28 days and tended to be steady after 90 days. The development of autogenous shrinkage of SFRLAC reduced with the increasing water-to-binder ratio and by using the expanded shale with higher soundness and good water absorption, especially at early age within 28 days; the later drying shrinkage was reduced and the development of drying shrinkage was slowed down with the increasing volume fraction of steel fiber obviously; manufactured sand led to less autogenous shrinkage but greater drying shrinkage than fine lightweight aggregate in SFRLAC. The regularities of autogenous shrinkage and drying shrinkage of SFRLAC expressed as the series of hyperbola are analyzed.

A prediction model for autogenous shrinkage of high-performance concrete in bridge engineering

Based on an experimental method of studying the autogenous shrinkage of high-performance concrete (HPC) in a mould of low-density flexible corrugated pipe, this paper presents experimental results and a prediction model for autogenous shrinkage of HPC with respect to water to cementitious materials ratio, replacement ratio of fly ash, air content and aggregate to cementitious materials paste ratio. Reasonably good agreement is observed between the experimental and predicted autogenous shrinkage, thus indicating that the proposed model can be successfully used to estimate the effects of the studied parameters on the development of autogenous shrinkage in HPC.

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.

Estimation of temperature effects on autogenous shrinkage of concrete by a new prediction model

To accurately estimate the temperature effects on autogenous shrinkage of concrete, a new prediction model based on time–temperature dependent activation energy is proposed in this study. For this purpose, a series of autogenous shrinkage tests are performed considering different water to cementitious materials ratios and curing temperatures. Results revealed that the temperature dependency of autogenous shrinkage cannot be described solely by the simple time shift of the existing maturity method. In particular, maturity cannot incorporate the cross-over effect of autogenous shrinkage by which later age autogenous shrinkage of concrete, subjected to low curing temperature, usually exceeds the autogenous shrinkage of concrete subjected to relatively high curing temperature. Therefore, to overcome the shortcomings of the maturity method, a new prediction model based on time–temperature dependent activation energy is proposed. Reasonably good agreement is observed between experimental and predicted autogenous shrinkage, thus indicating that the proposed prediction model can be successfully used to estimate the time–temperature effects in the development of autogenous shrinkage. However, the absolute value of autogenous shrinkage strain still cannot be obtained from the proposed model, because the model gives only the development of autogenous shrinkage. Therefore, a prediction model for the absolute value of autogenous shrinkage is needed in order to obtain predicted autogenous shrinkage strain.