Drying shrinkage of expansive cements (original) (raw)
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An overview on the effect of internal curing on shrinkage of high performance cement-based materials
Construction and Building Materials, 2017
High performance cement-based materials, such as high or ultra-high performance concrete (HPC or UHPC) have been widely used and still faces the risk of cracking caused by shrinkages, especially autogenous shrinkage. Internal curing is an effective method to reduce or even eliminate autogenous shrinkage and has effects on chemical shrinkage, dry shrinkage, etc. The commonly used internal curing materials include super-absorbent polymer (SAP) and porous materials. Porous materials refer to lightweight aggregate (LWA) and porous superfine powders. In this paper, the internal curing materials has been divided into two categories based on water absorbing mechanism. The effects of these two categories of internal curing materials on shrinkage of high performance cement-based materials are reviewed. The addition of internal curing materials releases internal curing water, postpones the drop of internal RH, and reduces autogenous shrinkage, but increase chemical shrinkage. The addition of internal curing materials with extra water increases drying shrinkage. The mechanisms of shrinkage on internal curing are also summarized and discussed. However, those mechanisms only focus on certain type of shrinkage. To reduce the risk of cracking more effectively, the relationship of different type of shrinkages should be established.
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.
Preliminary Investigation of Drying Shrinkage Cement Paste Specimens
In order to perform drying shrinkage observations in ESEM (Environmental Scanning Electron Microscope), a preparation procedure for cement paste samples is developed. Instead of casting standard prisms (40 x 40 x 160 mm3), cement paste samples were cast in specially designed moulds of 30 x 30 x 2 mm3 and 10 x 10 x 2 mm3 in size. A special cylindrical tool was developed for polishing samples to the thickness of 1 mm or less. The sample observations as well as digital images of samples are acquired in ESEM. Images are analyzed to obtain displacements of the points of the cement paste samples due to the drying shrinkage.
Transportation Research Record: Journal of the Transportation Research Board, 2008
This paper demonstrates the difference in the shrinkage behavior of a sealed concrete that undergoes self-desiccation and an unsealed concrete that experiences external drying in addition to the selfdesiccation. The performance of SRA and LWA depends significantly on boundary conditions of concrete (i.e., sealed versus unsealed), which must be considered when selecting a shrinkage mitigation strategy.
Drying Shrinkage Mechanisms in Portland Cement Paste
Journal of the American Ceramic Society, 1987
The shrinkage mechanisms of portland cement paste were investigated from shrinkage, weight loss, and pore structure measurements using nitrogen sorption and mercury intrusion porosimetry (MIP). Thin samples (2.3 mm) of well-hydrated (165 d) pastes of 0.4 and 0.6 water-to-cement (W/C) ratios were dried directly from saturated surface dry state to 75%, SO%, 11%, and 0% relative humidity (rh). From equilibrium shrinkage vs calculated increase in surface free energy curves two active stress mechanisms were identified. The Gibbs-Bangham (surface free energy) effect is the major stress mechanism, which is active in the entire rh range investigated, whereas the capillary stress effect is active above 25% rh. From elastic modulus calculations it can be concluded that true Gibbs-Bangham shrinkage accounts for only 33% of total first drying shrinkage. Thus nearly 67% of first drying shrinkage may be due to a decrease in interlayer spacing caused by Gibbs-Bangham and capillary induced stresses. Further, nitrogen measures the true external surface area, and total external pore volume can be obtained from combined measurements using nitrogen sorption and MIP.
MATEC Web of Conferences, 2018
The ambient temperature records in Iraq show a large variation between day and night reaching 20 C, depending on the season, whether it is summer or winter. For this reason, the aim of this research is to study the effect of these conditions on the drying shrinkage of self-compacting concrete produced by using Portland-Limestone cement (ASTM C595-Type IL). SCC mixes were designed to attain compressive strengths of 40 and 60MPa at 28days with and without silica fume respectively. Same mixes were reproduced with ordinary Portland cement (ASTM C150-Type I) for comparisons. Two maximum sizes of aggregate 10 and 20 mm were incorporated in this work. The drying shrinkage was measured for 180 days after 7 days of water curing. The range of ambient (outdoor) temperature variation was from-4 to + 39 o C and the relative humidity ranged from 15 to 60 %. The results of this exposure were compared to that of specimens kept in the shrinkage chamber, with a temperature of 21 o C and relative humidity 35%. The current results showed that due to the irreversible nature of shrinkage strain, the drop of ambient temperature and the rise of atmosphere moisture or relative humidity would not reverse the shrinkage strain. It is important to figure the final total accumulated strain when dealing with ambient temperature variation. The drying shrinkage characteristics for concrete made with Type IL cement, are found similar to that for concrete produced with Type I cement.
IRJET, 2022
Through its lifespan, concrete undergoes several physical and chemical changes, which normally led to shrinkage of concrete, especially at an early age, when the initial hydration processes take place. The shrinkage of concrete at an early stage of hardening may lead to the initial formation of cracks that vary in shape and size and depends on the concrete constituents and surrounding conditions, including temperature and/or the moisture state that may lead to volumetric deformation 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 the shrinkage behavior of cement concrete incorporated with different mineral admixtures and fibers.
IRJET, 2022
Volumetric shrinkage occurs frequently in cement-based materials, which may cause tensile strains and cracking. The volume changes brought on by water evaporation are known as shrinkage. Volume variations in concrete can happen early in the material's life or later on. Plastic shrinkage occurs at the plastic stage of concrete. The change in volume after the setting has occurred is known as drying shrinkage. Autogenous shrinkage is the shrinking that occurs in a conservative system, or one in which moisture cannot migrate into or out of the paste. This study tries to examine the impact of various SCMs such as fly ash, GGBFS, silica fume, etc. and fibers such as steel fiber, polypropylene fiber, glass fiber, etc. in the shrinkage characteristics of concrete.
Effect of Shrinkage Reducing Admixture on Drying Shrinkage of Concrete with Different w/c Ratios
Materials
The reduction of the moisture content of concrete during the drying process reduces the concrete’s volume and causes it to shrink. In general, concrete shrinkage is a phenomenon that causes concrete volume to dwindle and can lead to durability problems. There are different types of this phenomenon, among them chemical shrinkage, autogenous shrinkage, drying shrinkage including free shrinkage and restrained shrinkage, and thermal contraction. Shrinkage-reducing admixtures are commercially available in different forms. The present study investigates the effect of liquid propylene glycol ether on mechanical properties and free shrinkage induced by drying at different water-cement (w/c) ratios. Furthermore, the effect of shrinkage-reducing admixtures on the properties of hardened concrete such as compressive and tensile strength, electrical resistivity, modulus of elasticity, free drying shrinkage, water absorption, and depth of water penetration was investigated. The results indicated ...
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.