Mechanism of early age shrinkage of concretes (original) (raw)
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Five year drying of high performance concretes: Effect of temperature and cement-type on shrinkage
Cement and Concrete Research, 2017
This experimental study imposes limited relative humidity (RH) gradients to small mature concrete samples, at a constant temperature T = 20, 50 or 80°C. Mass loss and shrinkage are recorded until stabilization at each RH and T, for up to 1991 days. Firstly, our mass loss data are consistent with those presented in former research (on different samples of the same batch). After presenting and analyzing shrinkage kinetics, experimental data are fitted with usual models for shrinkage prediction, at each temperature of 20, 50 and 80°C. An adequate match is obtained by combining capillarity (i.e. Vlahinic's model coupling poro-elastic constants and water saturation level) and desorption (Bangham's equation). Subsequently, relative mass variation (RMV) is plotted against shrinkage ε sh dry data. Three distinct phases are obtained at 20 or 50°C and down to 30%RH; up to four distinct phases are observed at T = 80°C and down to 12%RH. The latter are confirmed by experiments on (60°C; 7%RH) dried concrete. The four phases in the (RMV ε , sh dry) diagram are interpreted against shrinkage data on mature cement paste dried at 60°C; 7%RH and against the literature.
Effect of Curing Methods on Early-Age and Drying Shrinkage of High-Performance Concrete
Transportation Research Record, 2003
Many engineers and agencies observed that field implementation of HPC is highly dependent on curing and placing conditions. In particular, early-age properties and their relationships to the long-term durability as well as the effect of pozzolanic material, such as silica fume and fly ash, on the early-age as well as drying shrinkage is also needed. The objective of this paper is to present results of a study performed to identify the effect of various curing methods on the early-age (autogenous) as well as drying shrinkage of normal as well as lightweight high performance concrete (HPC). The study included a comparison of available analytical models for predicting early age as well as drying shrinkage with results from tests performed on different mixes. HPC mixes were developed and evaluated as part of an overall study for the New Jersey Department of Transportation (NJDOT) to develop and implement mix design and technical specifications for HPC transportation structures, such as pavements and bridges. In this paper, the effect of using three different curing methods on the early age performance of highperformance concrete is presented. The curing conditions consisted of 1) Air-dry curing; 2) Burlap or moist curing; and 3) Curing compound. Results show that moist curing (Burlap) should be applied within one hour after placing of concrete to improve early-age performance. For very low w/c+p ratio, fly ash and light weight aggregate improved the autogenous shrinkage performance. Moreover, current shrinkage models need to be revised to address HPC mixes.
Effect of curing temperature and type of cement on early-age shrinkage of high-performance concrete
Cement and Concrete Research, 2001
This paper presents the results of an experimental study on the influence of curing temperature and type of cement [Portland cement and blast-furnace slag (BFS) cement] on the autogenous deformations and self-induced stresses in early-age concrete. It was found that higher temperatures do not lead to higher deformations in the observed period, but generally cause a faster shrinkage and a faster development of self-induced stresses. Another experimental finding is that, at the temperatures tested, concrete made with BFS cement shows higher shrinkage in the first days than concrete made with Portland cement.
Aci Materials Journal
The very high mechanical strength and enhanced durability of ultra highperformance concrete (UHPC) make it a strong contender for several concrete applications. However, UHPC has a very low water-to-cement ratio, which increases its tendency to undergo early-age shrinkage cracking with a risk of decreasing its long-term durability. To reduce the magnitude of early-age shrinkage and cracking potential, several mitigation strategies have been proposed including the use of shrinkage reducing admixtures, internal curing methods (e.g. superabsorbent polymers), expansive cements and extended moist curing durations. To appropriately utilize these strategies, it is important to have a complete understanding of the driving forces behind early-age volume change and how these shrinkage mitigation methods work from a materials science perspective to reduce shrinkage under field like conditions. This dissertation initially uses a first-principles approach to understand the interrelation mechanisms between different shrinkage types under simulated field conditions and the role of different shrinkage mitigations methods. The ultimate goal of the dissertation is to achieve lower early-age shrinkage and cracking risk concrete along with reducing its environmental and economic impact. As a result, a novel environmentally friendly shrinkage reducing technique based on using partially hydrated cementitious materials (PHCM) from waste concrete is proposed. The PHCM principle, mechanisms and efficiency were evaluated compared to other mitigation methods.
Autogenous Shrinkage of Concrete at Early Ages
Lecture notes in civil engineering, 2019
High Performance Concrete (HPC), particularly high strength concrete mixes (60-100MPa) containing high cementitious content and low w/b ratios (0.40-0.25) is used for some precast elements. Ultra High Performance Concrete (UHPC) up to 200MPa containing very high cementitious content and very low w/b ratios (0.25-0.17) is also used for precast and prestressed elements in buildings and bridges. Shrinkage characteristics of HPC and UHPC differ considerably from those of conventional concrete. Due to their high cementitious content and low w/b ratios, the drying shrinkage component is significantly smaller when compared with the autogenous shrinkage component. HPC and UHPC elements, when steam-cured, undergo majority of their shrinkage within a few days of casting. In this paper, mechanisms of autogenous shrinkage of HPC and UHPC at early ages are compared under different curing conditions. Contribution of autogenous shrinkage and drying shrinkage components on the total shrinkage is discussed. At very early ages, plastic shrinkage and plastic settlement cracking and factors affecting them for HPC and UHPC are also outlined.
Effect of drying conditions on autogenous shrinkage in ultra-high performance concrete at early-age
Materials and Structures, 2011
This experimental study investigated the effects of drying conditions on the autogenous shrinkage of ultra-high performance concrete (UHPC) at early-ages. UHPC specimens were exposed to different temperatures, namely, 10, 20 and 40°C under a relative humidity (RH) ranging from 40 to 80%. The effects of using a shrinkage-reducing admixture (SRA) and a superabsorbent polymer (SAP) as shrinkage mitigation methods were also investigated. The results show that autogenous and drying shrinkage are dependent phenomena. Assuming the validity of the conventional superposition principle between drying and autogenous shrinkage led to overestimating the actual autogenous shrinkage under drying conditions; the level of overestimation increased with decreasing RH. Both SRA and SAP were very effective in reducing autogenous shrinkage under sealed conditions. However, SRA was efficient in reducing drying shrinkage under drying conditions, while SAP was found to increase drying shrinkage. Generally, results indicate that adequate curing is essential for reducing shrinkage in UHPC even when different shrinkage mitigation methods are applied.
Effect of materials and curing period on shrinkage of concrete
The ASTM C157 free shrinkage test is used to evaluate the effects of mix proportioning parameters and curing on concrete shrinkage with the goal of providing recommendations that will reduce concrete shrinkage in bridge decks. Specimens are dried up to 365 days at 23 ± 2 o C (73 ± 3 o F) and 50 ± 4 percent relative humidity. Parameters include aggregate content; cement fineness; water-cement ratio; curing period; partial cement replacement by slag, Class C fly ash, or silica fume; superplasticizer dosage; the use of a shrinkage reducing admixture; and aggregate type. The results indicate that increasing the aggregate content (decreasing the paste content) of a concrete mix decreases shrinkage and that water-cement ratio has little effect in and of itself. For a given aggregate content and water-cement ratio, concretes made with Type I/II cement shrink more than concretes made with Type II coarse-ground cement. Concrete containing a 30 percent cement replacement (by volume) of either Class C fly ash or granulated ground blast-furnace slag exhibit higher shrinkage than concrete with only Type I/II cement when cured for three days. Limestone coarse aggregate produces concrete with higher shrinkage than concrete made with quartzite coarse aggregate. Increased curing periods lead to a decrease in shrinkage for concretes made with either Type I/II or Type II coarse-ground cement. No consistent effect of dosage rate on shrinkage was observed for concretes made with the superplasticizers tested. The use of a shrinkage reducing admixture at a dosage rate of 2 percent by weight of cement reduced the shrinkage of concrete nearly iv 32 percent after 365 days. The shrinkage reducing admixture, however, produced concrete that at times exhibited an unstable air content.
Shrinkage Behavior of Conventional and Nonconventional Concrete: A Review
Civil Engineering Journal
Concrete is indeed one of the most consumed construction materials all over the world. In spite of that, its behavior towards absolute volume change is still faced with uncertainties in terms of chemical and physical reactions at different stages of its life span, starting from the early time of hydration process, which depends on various factors including water/cement ratio, concrete proportioning and surrounding environmental conditions. This interest in understanding and defining the different types of shrinkage and the factors impacting each one is driven by the importance of these volumetric variations in determining the concrete permeability, which ultimately controls its durability. Many studies have shown that the total prevention of concrete from undergoing shrinkage is impractical. However, different practices have been used to control various types of shrinkage in concrete and limit its magnitude. This paper provides a detailed review of the major and latest findings rega...