Pre-wetted Lightweight Fine Aggregate Research Articles

Effect of multi-minerals on the mechanical behavior and pore structure of fiber reinforced internal-cured green concrete

In this study, multi-minerals were incorporated in fiber reinforced internal-cured green concrete (FRICC) to achieve both an improvement in concrete performance and environmental sustainability. The effect of multi-minerals on FRICC with pre-wetted lightweight fine aggregate (LWFA) and basalt-polypropylene (BF-PF) fiber was investigated through examining compressive and flexural strengths, flexural toughness, microstructure, pore structure and CO2 emissions. In comparison to ordinary concrete (mixture PO), FRICC presented good flexural performance but a decreased compressive behavior with an increase of 20.5% in flexural strength and a minor decrease of 1.6% in compressive strength. With the addition of multi-minerals, an enhancement in fiber-strengthening and anti-cracking performance was achieved, presenting a positive effect on concrete's strengths, post-cracking manner and pore structure. The internal curing of pre-wetted LWFA stimulated the pozzolanic reaction of minerals given that a denser microstructure with less porosity and more C–S–H gel effectively bound with aggregates and BF-PF fiber was identified. FRICC with a ternary mix of minerals (10% fly ash, 10% blast furnace slag and 5% metakaolin) exhibited the best mechanical performance and pore structure with an increase of 19.6% and 19.2% in compressive and flexural strength, respectively, and a decrease of 29.3% and 13.6% in porosity and mean pore diameter, respectively. Additionally, a reduction in CO2 emissions of up to 19.7% was achieved through adding multi-minerals. In general, the incorporation of multi-minerals brings positive consequences to both the performance of FRICC and environmental sustainability.

Internal Curing Efficiency of Pre-Wetted Lightweight Fine Aggregates on Strength Parameters of Concrete

Internal cured concrete (ICC) using pre-wetted lightweight aggregates is to replace conventional type of curing. Normally curing for conventional type is done by external to internal, which requires a large membrane and a large amount of water is required to do this type of procedure and the water which we use for curing may get runoff or get evaporated. But in ICC type of curing it cure inside to outside, the pre-wetted lightweight aggregates provides sufficient moisture to hydrate cement inside the concrete. The pre-wetted light weight aggregates, which stores water inside and acts as a reservoir. It release water when hydration process is done. Lightweight aggregates such as expanded clay or shale, vermiculite, pumice, slate, perlite having high water absorbing capacity are generally used for internal cured concrete. In this study, vermiculite and expanded clay had been used as replacements of fine aggregate, 2.5%, 5%, 7.5%, 10% and 12.5% are replaced for vermiculite and 5%, 10%, 15%, 20% and 25% for expanded clay.

Field-Observed Cracking of Paired Lightweight and Normalweight Concrete Bridge Decks

Research has suggested that conventional lightweight concrete can offer durability advantages due to reduced cracking tendency. Although a number of publications exist providing the results of laboratory-based studies on the durability performance of lightweight concrete (with lightweight coarse aggregate) and internally cured concrete (using prewetted lightweight fine aggregate), far fewer field studies of durability performance of conventional lightweight concrete bridge decks in service have been performed. This study was commissioned to provide insight to a highway agency on whether enhanced durability performance, and therefore reduced maintenance and longer lifecycles, could be anticipated from existing lightweight concrete bridge decks that were not intentionally internally cured. To facilitate performance comparison, each lightweight bridge deck selected for inclusion in this study was paired with a companion normalweight bridge deck on a bridge of similar structural type, deck thickness, and geometric configuration, with similar age, traffic, and environmental exposure. The field-observed cracking of the decks was recorded and evaluated, and crack densities for transverse, longitudinal, and pattern cracking of the normalweight and lightweight deck in each pair were compared. Although some trends linking crack prevalence to geographic location, traffic, and age were observed, a distinct difference between the cracking present in the paired lightweight and normalweight bridge decks included in this study was not readily evident. Statistical analysis using analysis of covariance (ANCOVA) to adjust for age and traffic influence did not indicate that the type of concrete deck (lightweight or normalweight) is a statistically significant factor in the observed cracking. Therefore, for these service environments, lightweight decks did not consistently demonstrate reduced cracking.

Integrated shrinkage, relative humidity, strength development, and cracking potential of internally cured concrete exposed to different drying conditions

ABSTRACT Internal curing (IC) technology using prewetted lightweight fine aggregates (LWFAs) as additives has been proved an effective means for mitigating both autogenous shrinkage and early-age cracking under sealed curing conditions. However, for practical structures in the field, concrete experiences more complex environmental conditions compared to under sealed curing. To better utilize internal curing technology for durable concretes, this study conducts comprehensive investigations on both control and internally cured concretes at water/cement (w/c) ratio of 0.3 and 0.4 in terms of the influence of age when concrete is exposed to drying and the drying duration on the developments of integrated shrinkage, internal relative humidity, compressive and flexural strengths, mass loss, and cracking potential. The results are beneficial for producing internally cured concrete with increased resistance to early-age cracking and enhanced durability for infrastructure applications.

Internal Curing for Concrete Bridge Decks: Integration of a Social Cost Analysis in Evaluation of Long-Term Benefit

Internal curing is a new approach to the proportioning of concrete mixtures in which a portion of the fine aggregate in concrete is replaced by prewetted lightweight fine aggregate. Internally cured concrete has the potential to extend the service life of bridge decks substantially because of reduced cracking and chloride ingress. Although internally cured concrete has been used, its use is limited because of the slight increase in the initial cost and need for an understanding of batching operations and performance of quality control. Even though some cost–benefit studies have been performed, the potential life-cycle benefits of internal curing may be significantly underestimated because the social costs (network traffic disruptions) have not been integrated into previous studies. This study evaluated the total life-cycle benefits of bridge decks made of high-performance concrete with internal curing (HPC-IC) by a comparison of such bridge decks with bridge decks made of normal concrete (NC). Three bridges on an Interstate highway, an arterial road, and an urban connector were selected to examine the total life-cycle costs of bridge decks made of NC, high-performance concrete, and HPC-IC. The results suggest that the total life-cycle costs of bridge decks made of HPC-IC might be reduced by 50% compared with those of bridge decks made of NC and that the scale of reduction of social costs depends on the bridge traffic volume. The study provides insights that relevant decision makers can use to determine whether the internal curing process should be used in bridge deck management activities so that limited resources can be more effectively allocated on the basis of the potential benefits.

Freezing and Thawing Behavior of Internally Cured Concrete

Abstract The paper presents results from an experimental investigation on the freezing and thawing behavior of internally cured concrete. Air-entrained internally cured concrete was tested in a series of mixtures. The internally cured concrete was designed where a portion of the normal-weight fine aggregate was replaced with an equivalent volume of pre-wetted lightweight fine aggregate. The internally cured concrete was then exposed to cyclic freezing and thawing following the ASTM C666A procedure. This work was performed to determine whether properly designed, internally cured, air-entrained concrete may have an increased susceptibility to freeze–thaw damage. It is shown that when concrete is designed with a low water/cement ratio (w/c) (approximately 0.42 or lower) and a volume of internal curing water is added to match the chemical shrinkage volume, the internally cured concrete mixtures showed a very low potential for freeze–thaw damage (comparable to that of conventional concrete). The work did show that when water remains in the lightweight aggregates (because of a higher w/c that may not draw the water from the aggregate or when substantially more internal curing water is used than necessary), freeze–thaw damage may occur.

Using Drinking Water Treatment Waste as a Low-Cost Internal Curing Agent for Concrete

Results from a preliminary study that investigated the potential of using drinking water treatment waste sludge as an internal curing agent for concrete are presented. The concept consists of using the high water content, primarily calcium carbonate material, as a concrete admixture. Two other commonly used internal curing agents - prewetted lightweight fine aggregate and a superabsorbent polymer - were investigated as a comparison. Cement mortars were tested for compressive strength, degree of hydration, and shrinkage. Micrographs of mortars containing the three different internal curing agents were compared visually to evaluate the distribution of internal curing agents and relative hydration. Results show that drinking water treatment waste is an effective internal curing agent, improving cement hydration, compressive strength, and mitigating autogenous shrinkage.

Effect of Internal Curing on Moisture Gradient Distribution and Deformation of a Concrete Pavement Slab Containing Pre-Wetted Lightweight Fine Aggregates

Internal curing technology has been proven effective in improving many properties of concrete. The application of this technology to the transportation infrastructure holds promise with increasing resistance to cracking and enhanced durability. On the other hand, an investigation of moisture distribution in concrete slabs is of significance for predicting slab deformation and the associated stress and failure. This study is performed to investigate the characteristics of the pre-wetted sintered fly ash lightweight fine aggregate (LWFA) used as an internal curing agent and the influence of internal curing on concretes exposed to sealed curing, external drying, and surface wetting conditions. The internal curing effects on the moisture distributions in concrete pavement slabs at w/c = 0.3 and 0.4 were evaluated through experimental measurements, and the effects on slab deformations were quantified using an equivalent temperature difference. The findings of this study will benefit the further application of internal curing technology to the transportation infrastructure's construction.

Fluid transport in high volume fly ash mixtures with and without internal curing

The transport of fluid and ions in concrete mixtures is central to many aspects of concrete deterioration. As a result, transport properties are frequently measured as an indication of the durability that a concrete mixture may be expected to have. This paper is the second in a series investigating the performance of high volume fly ash (HVFA) mixtures with low water-to-cementitious ratios (w/cm) that are internally cured. While the first paper focused on strength and shrinkage, this paper presents the evaluation of the transport properties of these mixtures. Specifically, the paper presents results from: rapid chloride migration (RCM), rapid chloride penetration test (RCPT), apparent chloride diffusion coefficient, surface electrical resistivity, and water absorption. The test matrix consisted of mortar samples with two levels of class C fly ash replacement (40% and 60% by volume) with and without internal curing provided with pre-wetted lightweight fine aggregates (LWA). These mixtures are compared to plain ordinary portland cement (OPC) mortars. The results indicate that HVFA mixtures with and without internal curing provide benefits in terms of reduced transport coefficients compared to the OPC mixtures.

Internal Curing Efficiency of Prewetted LWFAs on Concrete Humidity and Autogenous Shrinkage Development

Internal curing (IC) technology using prewetted lightweight fine aggregates (LWFAs) as additives has been proved an effective means for mitigating both autogenous shrinkage and early-age cracking under the sealed-cured conditions. However, complete elimination of autogenous shrinkage may not be necessary, as negative effects, such as the durability problems, might be induced by an excessive amount of LWFAs introduced. To better utilize internal curing technology for durable concretes, this study investigates the microstructure and the desorption properties of sintered fly ash and expanded shale LWFAs. The influences of these two types of LWFAs on autogenous shrinkage and internal RH development were experimentally evaluated in concrete with w/c of 0.3 and 0.4. The internal curing efficiency, defined as the relative volume ratio of LWFAs in paste matrix as compared to that used for completely mitigating autogenous shrinkage, is a function of particle size and spacing of LWFAs. The results show that 100% internal curing efficiency (no autogenous shrinkage at the age of 28 days) can be achieved if the ratio of the LWFA particle/paste proximity and the particle size (2L=hRi) approach 1.1. DOI: 10.1061/(ASCE)MT.1943- 5533.0000883. © 2014 American Society of Civil Engineers.

Salt scaling resistance of highway concrete containing pre-wetted lightweight fine aggregate as internal curing agents

Internal curing technology using pre-wetted lightweight fine aggregates (LWFAs) as additives has been proved as an effective means for mitigating both autogenous shrinkage and early-age cracking under the sealed–cured conditions. However, concrete structures (i.e. pavements and bridge decks) can be subjected to severe environmental loadings such as de-icing salt and freeze/thaw cycles. In this study, the salt scaling-resistant properties are investigated on concretes containing two types of pre-wetted LWFAs as partial replacement of sand at water-to-cement ratio (w/c) of 0.3 and 0.4. The results reveal that concretes containing pre-wetted LWFA are more sensitive to salt scaling damage because of the higher degree of saturation of concrete and low strength of LWFA. The hydraulic and crystallisation pressures generated in the pores of LWFA might be the major contributor for the crushing of LWFA and the consequent damage in concrete. Air-entraining admixture must be used in the LWFA concrete in order to achieve sufficient frost resistance.

Internal Curing of Concrete Bridge Decks in Utah

The objectives of this research were (a) to monitor in situ bridge deck properties such as moisture and diffusivity for both conventional concrete and concrete containing prewetted lightweight fine aggregate, which is intended to provide internal curing; (b) to compare deck performance in terms of early-age cracking; and (c) to evaluate the compressive strength and chloride permeability of concrete mixtures in the laboratory using cylinders cast in the field at the time of deck construction. The research scope included four bridges—two constructed with conventional concrete and two containing prewetted lightweight fine aggregate—in northern Utah. Data from sensors embedded in the concrete decks indicated that the moisture content of the internally cured concrete was 2% to 3% higher at 28 days than the moisture content of the conventional concrete. Although the internally cured concrete had a higher moisture content, the electrical conductivity values were approximately the same for all decks after a few months; these values suggested that the two types of concrete had similar diffusivity. At 28 days, the average strength of the internally cured concrete was 1% higher than that of the conventional concrete, and the internally cured concrete passed between 2% and 30% less current during the rapid chloride permeability test than the conventional concrete. After 2 months, three to five cracks about 0.2 to 0.3 mm in width were found on each of the conventional concrete bridge decks, but no visible signs of cracking were found in the bridge decks with internal curing.

Simple Procedure for Determining Long-Term Chemical Shrinkage for Cementitious Systems Using Improved Standard Chemical Shrinkage Test

In the past 10 years, renewed research interest has shown the benefits of internal curing by incorporating prewetted lightweight fine aggregate (LWFA) in high-performance concrete (HPC). To determine the optimum LWFA content, information about the propensity for shrinkage in the cement paste, specifically the chemical shrinkage value, is needed. However, information is lacking on how to determine the long-term chemical shrinkage value for HPC with supplementary cementitious materials (SCMs) and/or shrinkage-reducing admixture (SRA). The purpose of this research was to identify a simple procedure to determine long-term chemical shrinkage values for given cementitious systems with SCMs and/or SRA. Several improvement to ASTM C1608 (dilatometry procedure) were investigated. An experimental prediction model was adopted and verified to estimate long-term chemical shrinkage values for portland cement systems containing SCMs and/or SRA. A recommended procedure is proposed to determine the long-term chemical shrinkage values for HPC systems containing SCMs and/or SRA, and a modification to a commonly used LWFA proportioning equation is suggested.

Scaling resistance of high performance concretes containing a small portion of pre-wetted lightweight fine aggregate

The subject of the investigation was the influence of pre-wetted lightweight aggregate on damage of the concrete surface due to cyclic freezing and thawing in the presence of de-icing salts tested according to the Swedish Standard SS 13 72 44 (the Boras method). Six series of concrete specimens were made with the same water/binder (w/b) ratio 0.32, cement volume 400 kg/m 3 and content of superplasticiser 8.8 kg/m 3 . One series, S3/2, contained an air-entraining agent. Series S4/7 and S4/8 were made with water/cement ratio equal to 0.45 and a lower cement content 340 kg/m 3 . In a few series the sand fraction 0-2 mm and basalt fraction 2-4 mm were partly or totally replaced by wetted lightweight aggregate. Concretes S3/1, S3/3, S4/7 and S4/8, failed the test. The best results were obtained for concrete S3/6 (with the 2-4 mm fraction replaced by half) and S3/2 (air-entrained). The application of an air-entraining agent is more expensive than LWA, and at a construction site it is not always easy to control. It seems that the replacement of a part of aggregate by LWA could be a more effective way to improve the scaling resistance. � 2004 Elsevier Ltd. All rights reserved.