Volume deformation of steam-cured concrete with fly ash during and after steam curing
TL;DR: In this article, a micromechanical model is proposed based on the capillary tension produced by pores, using interior humidity and hydration degree as the driving parameters, which decently predicts the total shrinkage and autogenous shrinkage of concrete specimens after steam curing.
About: This article is published in Construction and Building Materials.The article was published on 2021-11-01. It has received 10 citations till now. The article focuses on the topics: Shrinkage & Fly ash.
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TL;DR: In this article , the effect of 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, was studied.
7 citations
TL;DR: In this paper , the effects of steam curing conditions on concrete properties and microstructural characteristics are reviewed, and technical approaches such as appropriate raw material compositions and curing regimes are explored.
Abstract: In this paper, the effects of steam curing conditions on concrete properties and microstructural characteristics are reviewed, and technical approaches such as appropriate raw material compositions and curing regimes are explored. Moreover, the environmental effects of precast concrete are evaluated. The main conclusion is that steam curing can improve the early strength of concrete, but thermal damage, shrinkage cracking, delayed ettringite formation (DEF), and other factors cause the later strength to increase more slowly or even deteriorate. Accordingly, it is necessary to undertake methods for improvement: (1) Adopt a lot of high-activity mineral admixture + a few low-activity mineral admixture combinations to ensure that the early strength of concrete meets the standard while allowing the subsequent development of concrete hydration to ensure durability. (2) Control the precuring time and temperature gradient of the concrete to allow the initial structure of the concrete to form. (3) Use effective secondary curing, such as soaking in an aqueous solution of limestone, in addition to standard curing to further improve the compactness of concrete. Moreover, the replacement of cement with less than 30% mineral admixtures in steam-cured concrete should be promoted to alleviate the environmental hazards caused by excessive CO2 emissions.
4 citations
TL;DR: In this article , the hydration products and strength of cement pastes incorporated with ground blast furnace slag (GBFS) (0% and 20% replacement) have been investigated under steam curing condition (80 °C for 7 h and 7 d) in comparison with normal curing condition(moist curing for 28 d).
Abstract: The hydration products and strength of cement pastes incorporated with ground blast furnace slag (GBFS) (0% and 20% replacement) have been investigated under steam curing condition (80 °C for 7 h and 7 d) in comparison with normal curing condition (moist curing for 28 d). The results show that, during the initial 80 °C steam curing for 7 h, in addition to the filler effect, GBFS is still involved in cement hydration. The abundant available Al phase and Mg phase in GBFS promote the formation of flake-like hydrotalcite, foil-like C-(A)-S-H gels, as well as equant grain-shaped C-(A)-S-H gels. Prolonging the steam curing time to 7 d further improves the formation of hydrogarnet. Since the formation of both hydrogarnet and hydrotalcite can consume the available Al, steam curing for 7 d seems to favor the formation of low Al C-(A)-S-H gels. In addition, due to the formation of a large amount of hydration products, the influence of 20% GBFS addition on the demolding strength of initial steam-cured cement mortar (80 °C for 7 h) is almost negligible. However, further extending the steam curing time to 7 d increases the strength gap between 20% GBFS blended cement mortar and pure cement mortar, and the related mechanism is discussed.
2 citations
TL;DR: In this paper , the effect of graphite on alteration in properties of the cement compressive and tensile strength, Poisson's ratio, Young's modulus, porosity, and permeability for three days of curing was analyzed.
Abstract: Casing cementing is one of the most crucial operations in the oil well drilling process since it determines the durability and stability of the well throughout its life. Different additives have been mixed into the oil well cement slurry to improve the properties of both the cement slurry and the solidified cement sheath. Graphite is a waste material with a huge potential to be utilized in cementing to improve the properties of the oil well cement and reduce the graphite waste content in the environment. This study intends to analyze the effect of graphite on alteration in properties of the cement compressive and tensile strength, Poisson’s ratio, Young’s modulus, porosity, and permeability for three days of curing. Based on the trend of the properties during the three days of curing, equations were established to describe the future change in cement properties with time. Two formulas of cement, the base (with no graphite) and graphite-based (with 0.2% by weight of cement graphite) were prepared in this study. The results showed that the graphite successfully increased the compressive strength, tensile strength, and Poisson’s ratio of the cement sheath, throughout the curing process. Young’s modulus was decreased after the incorporation of graphite which indicates an enhancement in cement resistance to shear forces. The porosity and permeability were also decreased indicating formation of a more densified cement sheath.
1 citations
TL;DR: The use of fly ash as partial replacement of Portland cement in the production of environmentally-friendly concrete is now an established fact as discussed by the authors , and the authors of this study investigated the effects of class-C and class-F fly ash at 20 wt% replacement of PC on the strength and durability characteristics of concrete mixtures incorporating crushed stone sand as fine aggregate.
1 citations
References
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Journal Article•
1,024 citations
TL;DR: In this article, a method for reducing autogenous shrinkage in a material based on a hydraulic mineral binder, e.g. cement, by preparing a mixture comprising the binder and water and a water-entraining agent selected from the group consisting of hydrogels and microencapsulated water, casting the mixture in a desired configuration, and allowing the mixture to cure.
741 citations
TL;DR: In this paper, various mechanisms suggested to cause autogenous shrinkage are presented The mechanisms are evaluated from the point of view of their soundness and applicability to quantitative modeling of autogeneous shrinkage.
538 citations
TL;DR: In this paper, the relative humidity maintained over saturated and unsaturated salt solutions and of some salt hydrate mixtures have been collated from the literature over a wide range of temperature.
Abstract: The relative humidities maintained over saturated and unsaturated salt solutions and of some salt hydrate mixtures have been collated from the literature over a wide range of temperature. Results are presented for 38 saturated salt solutions, and details listed for salts which are recommended as suitable for humidity control. The control of humidity in the laboratory by the use of salt solutions is critically discussed.
515 citations
TL;DR: In this paper, the authors present a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage in concrete, including the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of the concrete, addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of water-entrained concrete.
Abstract: As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore network, the visco-elastic response of the developing solid framework, and the kinetics of the cementitious reactions. While the complexity of this phenomenon may hinder a quantitative interpretation of a specific cement-based system, it also offers a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of the cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of “water-entrained” concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches.
285 citations