Steam-cured Concrete Research Articles

Mechanical property, sorptivity and microstructure of steam-cured concrete incorporated with the combination of metakaolin-limestone

To explore the feasibility of using metakaolin and limestone in steam-cured concrete, mechanical property, sorptivity and microstructure of steam-cured concrete incorporated with the combination of metakaolin-limestone powder were studied, with steam-cured concrete incorporated with ground granulated blast furnace slag and fly ash as a reference. Due to the high reactivity of metakaolin, the presence of metakaolin reduces the heterogeneous distribution of hydration products, thereby resulting in a refined microstructure and lowered sorptivity of steam-cured concrete. The synergistic effect of metakaolin with limestone powder leads to further improvements on strength, sorptivity associated with a more uniform microstructure at late ages. Moreover, concrete incorporated with metakaolin-limestone powder and steam-cured at 40 °C can gain a comparable early strength (1 day) with concrete incorporated with the combination of ground granulated blast furnace slag - fly ash, and steam-cured at 60 °C; this indicates that the incorporation of metakaolin enables to reduce steam curing temperature without compromising early strength gain, which is of significance for mitigating steam-curing induced detrimental effects and reducing energy consumption.

Evolution of multi-scale pore structure of concrete during steam-curing process

Abstract Steam-curing at elevated temperature involves a complex hygrothermal coupling action, which greatly affects the hydration process, microstructure buildup and thus the mechanical and long-term properties of cement-based materials. This paper investigated the multi-scale pore structure characteristics of concrete, paste and paste-aggregate interfacial zone during steam-curing process by a combined method of microscopic image analysis, scanning electron microscopy and mercury intrusion porosimetry. The evolution model of pore structure of steam-cured concrete during steam-curing stage and corresponding mechanism are also discussed. The results show that the multi-scale pore structure evolution of concrete is remarkably influenced by the steam-curing process, which can be divided into three stages. The initial free water content is one of the critical factors affecting the pore structure evolution of steam-cured concrete, especially in the interfacial transition zone. The morphology of hydrated cement pastes in interfacial transition zone is looser than that of matrix. The expansion pressure of vapor in the heating period of steam-curing process when water interior expands more severely in a higher initial free water content hinders the precipitation and diffusion of hydrates, bringing a relative weaker interfacial transition zone for steam-cured concrete. A hydration degree-dependent and water to cement ratio-related theoretical model is established to characterize the pore structure evolution during steam-curing process, which is proved to be well consistent with the experimentally measured results.

Quantitative analysis of the influence of subfreezing temperature on the mechanical properties of steam-cured concrete

Abstract The precast structures prepared by steam-cured concrete have been increasingly used in order to speed up the construction of China’s High-Speed Rail and passenger dedicated lines in recent years. In the high-cold regions, such as Harbin, the precast concrete structures are exposed to continuous subfreezing temperature for several months every year. However, the influence of continuous subfreezing condition on mechanical properties of concrete has not been systematically investigated yet. According to the Laplace Equation and Gibbs-Duhem Equation, the theoretical size of minimal frozen pores and ice content in water-saturation concrete at −20 °C can be calculated. It is discovered that the change ratios of mechanical properties are related to the theoretical ice content in concrete. Phenomenological models between change ratios and ice content are established based on hyperbolic equations. Finally, the mechanism of phase transition of free water on mechanical properties is explained by means of classical fracture theory of concrete. In this research, a contrastive research was carried out under two temperature conditions of 20 °C and −20 °C on mechanical properties of steam cured concrete at 28 days, including compressive strength, flexural strength, dynamic modulus of elasticity and damping ratio. Experimental results obtained at −20 °C indicate that compressive strength, flexural strength and dynamic modulus of elasticity increase to some extent and damping ratio decreases. And the application of supplementary cementitious materials (fly ash and GGBS) on concrete has a significant impact on the variation ratio of mechanical properties under freezing temperatures. The results of micro structure by quantitative test reveal that the pore distribution was greatly optimized and the percent of harmful pore were substantially reduced by the supplementary materials of fly ash or GGBS.

Research on the resistance to saline soil erosion of high-volume mineral admixture steam-cured concrete

The reasonable steam curing regime and the resistance to saline soil erosion of high-volume fly ash steam-cured concrete, high-volume ordinary slag steam-cured concrete and high-volume ultra-fine slag steam-cured concrete were studied by determining the demoulding strength, reaction degree, strength development law, chloride ion permeability, connected porosity, and sulfate attack resistance. The results show that although high-volume fly ash steam-cured concrete with the ideal demoulding strength and good resistance to chloride ion permeability can be obtained via properly reducing water-binder ratio and simultaneously prolonging steam curing time, its later-age strength development and the resistance to sulfate attack are not significantly improved compared with plain cement steam-cured concrete. High-volume ordinary slag steam-cured concrete with both ideal demoulding strength and great strength development at later ages can be obtained via only appropriately prolonging the steam curing time. Ordinary slag tends to enhance the saline soil resistance of steam-cured concrete more significantly than fly ash. High-volume ultra-fine slag steam-cured concrete with the ideal demoulding strength and good resistance to chloride ion permeability and sulfate attack can be obtained without or via slightly prolonging the steam curing time. But ultra-fine slag does not have a better effect on the later-age performance of steam-cured concrete than ordinary slag. Compared with high-volume fly ash or ordinary slag steam-cured concrete with similar demoulding strengths, high-volume ultra-fine slag steam-cured concrete has the better resistance to saline soil erosion.

Volume Deformation Characteristics of Concrete Mixture during Thermal Curing Process

Expansion deformation of concrete mixture during steam curing process was a kind of unrecoverable volume expansion which would definitely affect the performance of concrete component. Because there were a few researches on expansion deformation of concrete mixture during thermal curing process, a new test method composed of constant temperature water bath, eddy current measurement sensor and data processing program was developed to measure the expansion deformation. The volume deformation characteristics of a typical concrete used for preparing track slab of China high-speed railway were investigated. Test results indicated that volume deformation of concrete mixture could be divided into 2 stages. One was rapid expansion at heating stage and another one was slow shrinkage at constant temperature stage. Besides, the addition of combination of flying ash, slag, nano-silica and nano-calcium carbonate was benefit for controlling the eventual expansion deformation during the whole thermal curing process. Study could be an important reference for heightening quality of steam-cured concrete.

Method of proportioning the cement-water ratio of steam-cured concrete

Method of proportioning the cement-water ratio of steam-cured concrete

Evaluation of sulfate resistance of slag contained concrete under steam curing

This paper mainly investigated the sulfate resistance of the slag incorporated concrete under steam curing. Concrete samples with different replacement ratios (0%, 20%, 50% and 70%) of slag under steam curing were exposed to 5% Na2SO4 solution for up to 540 days. Mass changes, open porosity and sulfate-ion contents of concrete were determined separately. Moreover, XRD, TGA, SEM and MIP were performed on the cement paste samples to investigate the landscape of their microstructures. The results showed that the variation of mass change lagged behind than that of open porosity. Steam curing increased the sulfate penetration and deterioration of the slag concrete. Interestingly, incorporation of 50% slag improved the sulfate resistance of standard-cured concrete and incorporation of 70% slag improved the sulfate resistance of steam-cured concrete. This was because a hydrotalcite type phase in the slag paste hindered the ettringite formation. However, the steam-cured concrete prepared with 20% and 50% slag experienced much worse deterioration, which was mainly due to the combined formation of ettringite and gypsum.

Effect of subsequent curing on surface permeability and compressive strength of steam-cured concrete

Steam curing is commonly used to produce the prefabricated elements to meet the requirement of the high early strength. However, this curing regime was proved to lead to the thermal damage on the microstructure and properties of concrete. And the subsequent curing after initial steam curing is critical to the development of performances of steam-cured concrete. In this study, four typical subsequent curing conditions simulating the extreme service environments were employed on the curing of steam-cured concrete. And the surface permeability indexes involving water and air permeations and compressive strength were measured to analyze the effects of subsequent curing condition on performance of steam-cured concrete. The results indicate that the surface permeability and strength development of steam-cured concrete are remarkably influenced by the subsequent curing condition. The subsequent curing such as long-term water-soaking curing at 20 °C or oven-dry curing at 60 °C deteriorates the performances of steam-cured concrete. Their surface permeability indexes are 75.1% and 88.0% higher than that of standard-cured concrete at 90 days, respectively. The continuous dissolution of calcium hydroxide is considered the main reason for deterioration of impermeability and strength of steam-cured concrete.

Durability Characteristics of High Early Strength Concrete

High early strength concrete (HESC) is a type of high performance concrete, which attains its specified strength earlier than normal concrete. This type of concrete is normally used in precast and prestressed concrete industries. Many studies have been performed on the production of high early strength concrete, but information on performance of high early strength concrete in durability tests is limited. This article deals with evaluation of durability index characteristics of high early strength concrete mixtures made with two different cements. Durability index tests such as oxygen permeability, sorptivity, rapid chloride permeability and water absorption tests were performed on three HESC mixtures made with two different cements and compared with a reference concrete. Our results reveal that high early strength concrete using steam curing is better than concrete produced using accelerator. The microstructural studies also revealed that steam-cured concrete is better than accelerator-cured concrete supporting the durability index properties of concretes tested.

Influence of cement and aggregate type on steam-cured concrete – an experimental study

The effects of aggregate and cement type on the properties of steam-cured concrete were explored. Ordinary Portland cement (OPC) and high early strength cement (HESC) were used as binders, and recycled and natural aggregates were used as inert mineral filler aggregates in the concrete. The developed concretes exhibited adequate levels of compressive strength after steam curing. Depending on the type of coarse and fine aggregates utilised, the concretes incorporating OPC developed 42–72% of their design strength after 1 d; the range was 52–83% for concretes made with HESC. At all ages, the HESC concretes had about 10% greater strength than the OPC concretes. Abrasion and skid resistance parameters were also determined. Although the concretes incorporating HESC and recycled aggregates had lower mechanical strength, the abrasion and skid resistance parameters were superior to the other mixtures, meaning they could be usefully utilised in pavement structures, flooring and slabs. With proper mixture proportioning, adequate strength can be achieved.

Effect of Type of Cement and Expansive Agent on the Hardening of Steam-Cured Concrete

Pre-cast concrete products are sometimes manufactured in two cycles daily. It is ensured that they have the required strength at an early stage of demolding by increasing the steam curing temperature to reduce cost or increase productivity. However, the reduction in durability because of cracking due to thermal stress is a topic of concern. On the other hand, it has been known that fine blast-furnace-slag powder and expansive agents show high temperature dependence. Although they are used even in precast concrete products, the effect of steam curing on these materials is not known. Thus, in this study, the expression of compressive strength and expansion that are critical in improving the quality and productivity of precast concrete products was investigated, using high early-strength cement and two types of expansive agents, namely, ettringite-based and lime-based agents. Consequently, the strength expression was accelerated by the addition of expansive agent to ordinary cement and high early-strength cement. The extent of restrained expansion is greater for the lime-based expansive agent than for the ettringite-based expansive agent, and when an expansive agent is added to high early-strength cement, the extent of restrained expansion falls to a level lower than that in the case of ordinary cement.

The mechanical characteristics of steam-cured high strength concrete incorporating with lightweight aggregate

In order to mitigate the thermal damage of steam curing process at elevated temperature on microstructure of concrete and thus prepare high quality steam-cured concrete, the effects of type and absorbing-water rate of lightweight aggregate on static and dynamic mechanical properties of steam-cured concrete were investigated by serials experiments in present paper. The temperature evolution of different positions in steam-cured concrete without and with lightweight aggregate during steam curing period was also tested. Result indicates that, compared to control sample without lightweight aggregate, the compressive strength of steam-cured concrete with 30% ceramsite sand replacing the same volume river sand is slightly higher while the one of sample with 30% expanded clay ceramsite is lower at 28-day age. Under the same compressive strength level, the static/dynamic elastic modulus of steam-cured concrete with 30% lightweight aggregate is lower than that of control sample, and the damping ratio of steam-cured concrete with 30% ceramsite sand is higher. Incorporation of lightweight aggregate into concrete will result in a delay of temperature rise, which is very important for alleviating the thermal damage of steam-cured concrete caused by elevated temperature at early age and thus is favourable of improving the compressive strength.

The Role of Phosphorus Slag in Steam-Cured Concrete

Steam curing is an effective method to increase the hydration degree of binder containing phosphorus slag. The role of phosphorus slag in steam-cured concrete was investigated by determining the hydration heat, hydration products, nonevaporable water content, pore structure of paste, and the compressive strength and chloride ion permeability of concrete. The results show that elevated steam curing temperature does not lead to new crystalline hydration products of the composite binder containing phosphorus slag. Elevating steam curing temperature enhances the early hydration heat and nonevaporable water content of the binder containing phosphorus slag more significantly than increasing steam curing time, and it also results in higher late-age hydration degree and finer pore structure. For steam-cured concrete containing phosphorus slag, elevating curing temperature from 60°C to 80°C tends to decrease the late-age strength and increase the chloride permeability. However, at constant curing temperature of 60°C, the steam-cured concrete containing phosphorus slag can achieve satisfied demoulding strength and late-age strength and chloride permeability by extending the steam curing duration.

蒸気養生を施したコンクリートの塩化物イオン浸透抵抗性

蒸気養生を施したコンクリートの塩化物イオン浸透抵抗性

不同水胶比下磷渣在蒸养混凝土中的应用

分别以普通纯水泥混凝土和高强纯水泥混凝土为对照组，在不改变蒸养制度的前提下，通过降低水胶比来提高掺磷渣的蒸养混凝土的拆模强度，并探究其后期抗压强度发展规律及抗氯离子渗透性。研究表明，在不改变水胶比时，掺入磷渣会显著降低蒸养混凝土的拆模强度；适当降低水胶比后，掺磷渣的蒸养混凝土的拆模强度接近甚至超过对照组，且后期具有较高的抗压强度增长速率和抗氯离子渗透性。 The ordinary plain concrete and high strength plain concrete were set as control samples. Decreasing water to binder ratio (W/B) was used to elevate the demolding strength of steam-cured concrete containing phosphorus slag under the same curing condition. The compressive strength and chloride ion penetration of steam-cured concrete containing phosphorus slag with decreased W/B were also investigated. The results show that addition of phosphorus slag decreases the de-molding strength of the concrete containing phosphorus slag with the same W/B as control sample. The demolding strength of concrete containing phosphorus slag with decreased W/B is close to or even higher than that of control sample. What’s more, the compressive strength development and chloride ion penetration resistance of the concrete containing phosphorus slag are higher than those of the control samples at late ages.

Influence of Steam Curing Method on the Performance of Concrete Containing a Large Portion of Mineral Admixtures

A comparison was made between the impact of raising the thermostatic temperature and the impact of prolonging the thermostatic time on the performance of steam-cured concrete containing a large portion of fly ash (FA) or ground granulated blast furnace slag (GGBS) by analysing the form removal strength, chemically combined water content, reaction degree, strength development, chloride permeability, and volume stability. For the materials and test conditions reported in this study, raising the thermostatic temperature is more favourable for concrete containing FA, as indicated by the significantly higher form removal strength and the higher growth of reaction degree of FA compared with prolonging the thermostatic time. With an increase in the thermostatic temperature, the hydration degree of a binder containing FA or GGBS initially increases and subsequently decreases. Although concrete containing FA can obtain satisfactory form removal strength with steam curing at 80°C, the late strength development of concrete containing FA is slow for the same curing conditions. The effect of the late performance of resistance to chloride ion permeability improved by FA is better than the effect improved by GGBS. The risk of destroying the structure of concrete containing a large portion of FA or GGBS due to delayed ettringite formation (DEF) is minimal when specimens were steam-cured at 80°C.

Evaluación del concepto de madurez en el hormigón con adición de cenizas de cascarilla de arroz

Steam curing is a process used to accelerate cement hydration reactions with the purpose of enhancing the mechanical strength of concrete at early ages, since hydration reactions are temperature dependent. To evaluate the influence of temperature on the development of mechanical properties of concrete the maturity concept was used. This method estimates the development of these properties according to the temperature history of concrete along the curing process. The temperature influence is indicated through the apparent activation energy (AE) value. The higher the AE value, the higher the energy amount will be necessary to start reactions, and thus the velocity of these reactions will be affected by temperature. This work is based on an experimental study of steam-cured concrete made with 5% and 10% of rice husk ash (RHA) addition in which the development of some mechanical properties was investigated. The rice husk ash used was obtained from uncontrolled combustion of rice husk, in an open chamber, without any temperature control or burning time. The mechanical property investigated was the compressive strength. Results indicate the influence of RHA addition and its dosage on the hydration reactions of cement and the mechanical properties of steam-cured concretes.

Experimental investigation on dynamic mechanical characteristics and microstructure of steam-cured concrete

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab. The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure. In the present paper, serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus, shear modulus, damping ratio, and microstructure of steam-cured concrete. The relationships between compositions, curing regime, microstructure, and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed. The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete. On the contrary, at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed. Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures. The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.

Influence of Metakaolin on Strength and Microstructure of Steam-Cured High-Strength Concrete

The influence of metakaolin (MK) on strength and microstructure of steam-cured high-strength concrete has been investigated using compressive strength test, XRD, MIP and SEM. Three MK replacement levels were considered in the study: 5%, 10% and 15% by weight of cement. A mix double blended with 10% MK and 10% slag was prepared too. Test results have indicated that MK can increase the compressive strength of steam-cured concrete, especially at early age. Compressive strength up to 90MPa at 1 and 28 days is obtained with the incorporation of 10% MK and 10% slag. When the replacement level of MK is higher than 10%, the enhancement of strength becomes less significant. Content of Ca (OH)2 crystals is decreased while content of hydrates with Al is increased due to the pozzolanic reactivity of MK. Concrete pore structure is significantly refined and a denser hydrates structure is obtained due to the pozzolanic reaction and filler effect of MK. Meanwhile, combination of aggregate and paste is enhanced too. The improvements of strength and microstructure become more obvious when MK and slag are double incorporated.

증기양생 콘크리트 표면상태에 대한 박리제의 영향 사례연구

증기양생 콘크리트 표면상태에 대한 박리제의 영향 사례연구