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This study uses neutron radiography (NR) and visual inspection to quantify water penetration in concrete samples exposed to water pressure on one face. It provides experimental data regarding the impact of mixture proportions on the hydraulic permeability of concrete. Specifically, it illustrates the influence of water-cement ratio (w/c), curing duration, entrained air content, and coarse aggregate (CA) size and volume on water transport. In addition, this paper quantifies the impact of permeability-reducing admixtures (PRAs) on water transport in concrete. It was observed that decreasing the w/c and/or increasing the curing duration reduced the fluid transport. Liquid and powder PRAs efficiently reduced fluid transport in concrete without impacting the compressive strength. The liquid PRA showed more consistent results, likely due to better dispersion than the powder PRA. Fluid ingress in concrete samples appears to increase with entrained air content due to a lower degree of saturation (DOS) at the start of the test. Increasing the CA volume fraction or decreasing the CA size will increase the fluid transport in concrete due to an increase in the connectivity of the interfacial transition zone. The influence of entrained air content, curing duration, CA volume fraction, and CA size was less noticeable on mixtures with PRAs due to the higher density and low permeability of these samples compared to control samples. [ABSTRACT FROM AUTHOR]

Self-healing is a process by which concrete is able to recover its properties after the appearance of cracks, which can improve mechanical properties and durability and reduce the permeability of concrete. Self-healing materials can be incorporated into concrete to contribute to crack closure. This study aims to evaluate the influence of crystalline admixtures and silica fume on the self-healing of concrete cracks. The rapid chloride penetration test was performed on cracked and uncracked samples, from which it was possible to estimate the service life of concretes. The concretes were characterized by tests of compressive strength and water absorption by capillarity. The use of crystalline admixtures did not have a negative influence on concrete properties, but did not favor the chloride penetration resistance. The concrete with silica fume showed the lowest charge passed and highest values of estimated service life. [ABSTRACT FROM AUTHOR]

Encapsulated admixtures in concrete have emerged as a prospective material to be used in future constructions. The core material is temporarily protected by the shell material, which also prevents the core from reacting with the concrete environment. The shell can be made of a pH-sensitive material that can deliver the core material based on the pH of environment rather than through mechanical rupture. The initial high alkaline nature of the concrete (pH 13.5) during the hydration and subsequent pH reducing conditions (by the environmental factors) can be used to design the delivery time of the core material. The coatings can be used to deliver the core material either within a short period or after a long period. The delivery of the core material at a desirable time can be achieved by the selection of a suitable coating agent. [ABSTRACT FROM AUTHOR]

An important part of improving the embodied carbon of the built environment is reducing carbon emissions associated with concrete. The long-term limitations around the availability of supplementary cementitious materials (SCMs) to replace portland cement have driven the search for additional innovative approaches. The beneficial use of carbon dioxide (CO2) in ready mixed concrete production has been developed and installed as retrofit technology with industrial users. An optimum dose of CO2 added to concrete as an admixture leads to the in-place formation of mineralized calcium carbonate (CaCO3) and can increase the concrete compressive strength. The improved performance can be leveraged to design concrete mixture proportions for a more efficient use of portland cement, along with the use of CO2 to reduce the carbon footprint of concrete. One producer has used the technology, starting in 2016, at over 50 plants. More than 3 million m3 of concrete have been shipped with an estimated net savings of 35,000 tonnes of CO2. The concrete produced with carbon dioxide is discussed in terms of the fresh and hardened performance, durability performance, and life cycle impacts. [ABSTRACT FROM AUTHOR]

Innovations are being developed with different additives in concrete mixtures to enhance their performance under certain conditions. This work models the split tensile strength through the electrical resistivity using a machine learning (ML) algorithm in different concrete mixtures. One of the most frequent nondestructive tests used on concrete is electrical resistivity (Er) for the simplicity of taking measurements on concrete elements. ML involves methods that provide solutions to advanced problems employing computational algorithms. This research employs a support vector regression algorithm, which can predict the split tensile strength value using a nondestructive test. The outcomes of this research exhibit a high correlation between electrical concrete resistivity and split tensile strength over 90%. Support vector regression algorithm achieves accuracy over 93% in the forecasting task. Of note is that the modified concrete contains starch as an addition to prove its performance compared to conventional concrete. [ABSTRACT FROM AUTHOR]

The present study investigates the impact of agro-green waste as an additive to concrete composition. The objective of the investigation is to evaluate the impact of agro-waste material as a thermal insulator for buildings. It helps in the reduction of energy consumption inside buildings. Wheat straw, rice husk, and coconut coir are used for the preparation of the composite concrete mixture. With a decrease in thermal conductivity and an increase in compressive strength, this paper provides a possibility of agro-waste in the concrete industry. [ABSTRACT FROM AUTHOR]

A mechanistic analysis is presented on the characteristics that would enable particles that form annulus voids when concrete freezes to be used as an alternative technology to air entrainment for protection of concrete from freezing-and-thawing damage. The paper introduces a concept of particle compliance and related equations to establish a fundamental basis for identifying and selecting particle types to use as additives in concrete to prevent freezing-and-thawing damage. Standard freezing-and-thawing testing confirms the results of the analysis and shows that the minimum quantity of particles needed to achieve a freezing-andthawing durable concrete varies with the particle type. Particle types such as polymeric hollow-core microspheres or polymeric solid-core particles would be insensitive to the factors that impact air entrainment obtained with surfactants, resulting in a more robust and reliable basis to consistently protect concrete from freezing-and-thawing damage. [ABSTRACT FROM AUTHOR]

The study aimed at examining the capacity of diverse add-ons in improving the self-healing ability of fiber-reinforced concrete through low water-cement ratios (w/c) and exposure to wide cracks. The self-healing capacities of crystalline admixture (CA) and silica fume (SF) were assessed by mechanical and durability performance. The effect of various exposure periods (7 to 42 days) in four different exposure conditions--namely, water immersion, wettingand- drying cycles, water contact, and air exposure (AE)--on selfhealing was evaluated by application of through-crack compressive stress. Compressive strength and durability analysis showed that CA with 10% SF was excellent in all four environments. Fouriertransform infrared spectroscopy and scanning electron microscope results showed significant bond formation contributing to the selfhealing property of the CAs. Therefore, concrete mixture with CA and 10% SF is recommended for use to increase the self-healing of concrete. [ABSTRACT FROM AUTHOR]

Cracks in bridge decks facilitate the penetration of chlorides that induce corrosion of reinforcing steel. Formation of cracks is related to the shrinkage and properties of the concrete and the restraints to movement. Lightweight concrete with a low modulus of elasticity, high creep, and water in the aggregate pores for internal curing has a reduced cracking potential. To control cracking, shrinkage of concrete can be reduced by using a shrinkage-reducing admixture (SRA). A recent study at the Virginia Department of Transportation (VDOT) investigated the performance of both lightweight concretes and concretes with SRA containing normalweight aggregates in the field and found that these concretes had no cracks or fewer cracks than were typical of decks constructed with normalweight aggregates over the past 20 years. VDOT developed a new specification that included lightweight concretes or concretes with normalweight aggregates and SRA and this specification is being used successfully to reduce cracking in bridge decks. This paper summarizes the work conducted to develop the new specification and includes information on field applications. [ABSTRACT FROM AUTHOR]

With adoption of winter maintenance strategies that typically include incorporation of aggressive deicer chemicals, pavement surfaces in cold regions are exposed to the risk of scaling damage. Reduced ride quality due to surface deterioration can eventually lead into a variety of maintenance and repair programs. Such pavement preservation programs impose significant charges to the owner agencies, while raising concerns regarding the safety issues associated with work zone areas. The present study addresses the correlation between surface hardness and concrete hardened properties. Moreover, factors that influence the concrete performance with respect to surface-abrasion resistance (hardness) were investigated. Of special interest was the relationship between surface hardness and concrete salt-scaling performance. An extensive investigation was carried out to assess the effects of various mixture proportions, curing regimes, and finishing times on surface hardness of the concrete specimens. In addition, compressive strength, depth-sensing indentation (DSI), and salt scaling tests were used to evaluate the correlation between concrete surface hardness and performance. A scaling quality classification table using abrasion mass loss values was developed. The results reflect further understanding of the relationship between abrasion resistance and salt scaling resistance that can cause defects when more than two cycles of abrasion testing are applied. [ABSTRACT FROM AUTHOR]

The effect of styrene-butadiene rubber (SBR) latexes on stability of semi-lightweight self-consolidating concrete and bond to embedded steel bars is not well understood. Five mixture series prepared with various lightweight aggregate (LWA) and SBR concentrations were considered in this project; the free water content was adjusted to secure compressive strength of 40 ± 3.5 MPa (5.8 ± 0.5 ksi). Test results have shown that SBR additions lead to reduced concrete flow velocity and passing ability; however, improved static stability such as bleeding and segregation. The bond properties to steel bars, particularly the initial stiffness of load versus slip curves, remarkably increased with SBR additions. This was related to the coupled effect of reduced concrete bleeding that promotes creation of hydration compounds at the steel-concrete transition zone and presence of SBR polymers that help relaxing stresses during loading. A series of regression statistical models was developed to predict the combined effect of free water, viscosity modifier, LWA, and SBR on stability and bond properties. [ABSTRACT FROM AUTHOR]

The article offers information on the long-term life of concrete structures exposed to marine environment. It mentions a modified theoretical model of chloride ion diffusion based on actual engineering combined with chloride ion diffusion theory; and also mentions the chloride ion diffusion data of concrete over 60 years, and it is very important to establish the life prediction model of concrete and design mixture ratio for marine concrete.

This paper focuses on the effects of fly ash on early-age mechanical and viscoelastic properties of concrete and on early-age cracking. Fly ash is a supplementary cementitious material that is mainly used to increase the durability of concrete. The effect on shrinkage-induced cracking of replacing some ordinary portland cement (OPC) with fly ash has not been studied previously. Material properties such as compressive strength, indirect tensile strength, and elastic modulus were measured with different percentage replacements of OPC with fly ash. Tensile creep and drying shrinkage were also measured on two types of specimens by using two different experimental techniques. The cracking age of plain concrete was observed by using a restrained ring test. Results revealed that the strength evolution of fly-ash-blended concrete is lower than the corresponding OPC concrete and the age at which restrained shrinkage cracking first occurs is also reduced. Slightly higher tensile creep coefficients were observed for fly-ash-blended concrete compared to OPC concrete, but drying shrinkage was not altered to any great extent. [ABSTRACT FROM AUTHOR]

The long-term effect of supplementary cementitious materials (SCMs) on alkali-carbonate reaction was evaluated using the concrete prism test for up to 10 years. None of the SCMs showed complete mitigation effects, although some types were more effective than others in reducing the expansion. Blending 10% reactive with 90% nonreactive aggregates was effective in meeting the 0.040% expansion limit at 1 year; however, the expansion was 0.074% after 10 years at room temperature. The chemical method for evaluating aggregate was found to give false negative or underestimate the potential expansion of blends of reactive and nonreactive aggregates. The use of SCMs with blends of aggregates that marginally meet the 1-year expansion limit provides some benefits in reducing the expansion at later ages. The concrete microbar test provides good correlations with the concrete prism test containing 100% reactive aggregates with and without SCM, but underestimates the expansion of blends of aggregates. [ABSTRACT FROM AUTHOR]

Chloride-based deicing salt solutions can react with the calcium hydroxide in the cementitious matrix, leading to the formation of calcium oxychloride. Calcium oxychloride formation has been implicated in the premature deterioration of pavement joints and concrete flatwork across cold regions in North America. This study examines the formation of calcium oxychloride in the presence of blends of different chloride-based deicing salts (sodium and calcium chloride). This evaluation was performed using several plain cementitious pastes and pastes with fly ash, slag, and silica fume used as supplementary cementitious materials. Fly ash and slag were used at 20% replacement levels and the silica fume was used at 3 and 6% replacement levels. Thermogravimetric analysis was used to quantify the amount of calcium hydroxide, and low-temperature differential scanning calorimetry was used to quantify the amount of calcium oxychloride formed. When the salt blends consist of less than 20% of calcium chloride by mass, the amount of calcium oxychloride that forms is low and does not depend on the calcium hydroxide content in the pastes. When the salt blends consist of more than 20% of calcium chloride by mass, the amount of calcium oxychloride that forms depends on the calcium hydroxide content in the paste and increases with calcium hydroxide content. This suggests two strategies to mitigate the amount of calcium oxychloride that is formed: reduction in the amount of calcium hydroxide in the pastes through use of supplementary cementitious materials, and the use of deicing salt blends that include lower amounts of calcium chloride. A model is developed to estimate the amount of calcium oxychloride formed in mixtures, given the calcium hydroxide and calcium chloride contents. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. The expansive nature of CSA-based cements can be used to enhance the resistance against shrinkage cracking by inducing compressive stress in concrete. Because of the higher water demand of CSA cement for achieving full hydration, as compared with ordinary portland cement (OPC), elevated water-cement ratios (w/c) for OPC-CSA cement blends are required for a successful mitigation of shrinkage. This study examines the effects of presoaked lightweight aggregate (LWA) addition on deformation properties of OPC-CSA mortar and concrete as an alternative to increasing the w/c. The motivation behind this work is to promote CSA hydration and increase the early-age expansion of OPC-CSA blends by curing concrete internally while avoiding the undesirable impacts of increased w/c on the microstructure of the mixture. The influence of LWA addition on autogenous and drying shrinkage of OPC-CSA blend was studied. It is shown that the early-age expansion of OPC-CSA blends can be dramatically increased when internal curing is implemented using LWA. Based on thermogravimetric (TG) results, it is indicated that the increase in expansion is partially due to the enhanced hydration of CSA cement in the mixture, which results in an increased rate of ettringite formation. Furthermore, the effects of LWA on total capillary porosity and compressive strength of OPC-CSA blends was also examined to verify the benefits of using LWA to promote CSA hydration as compared to increased w/c. [ABSTRACT FROM AUTHOR]

In this investigation, polymer concrete (PC) with three different epoxy resin contents, ordinary cement concrete (OCC), lightweight concrete (LWC), and lime-mortar soil (LMS) have been studied under uniaxial and triaxial compression tests to determine their mechanical behavior by measuring axial stress-strain and volumetric strain versus axial strain curves. According to the results, PC showed higher strength, ductility, and energy absorption than that of OCC and LWC. Then, nonlinear finite element analysis (NFEA) was implemented to predict the experimental results using hierarchical single-surface (HISS) failure criterion and disturbed state concept (DSC) to capture the elastoplastic behavior of concrete materials including volumetric strain. Moreover, the pattern of failure was estimated using ultimate disturbance values obtained from the model, followed by comparison with the experimental and Mohr-Coulomb failure patterns. The proposed model is applicable to a variety of materials with different behavior, and its prediction is in good accordance with experimental results. [ABSTRACT FROM AUTHOR]

Proper force transfer between reinforcement and surrounding concrete is one of the most significant factors affecting the structural performance of reinforced concrete. Because of the increasing interest in using fly ash and recycled concrete aggregate (RCA) in structural applications, it is necessary to investigate bond properties of mixtures proportioned with high volume of these materials. The present study investigates bond strength between concrete and reinforcing steel in full-scale beams constructed with various "green" concrete mixtures, including high-volume fly ash concrete containing 50% Class C fly ash replacement (FA50), concrete with 50% of coarse RCA replacement (RCA50), as well as a so-called "sustainable concrete" (SC) proportioned with 50% Class C fly ash and 50% RCA. Conventional concrete (CC) made without any fly ash and RCA is employed as the Reference mixture. Data obtained from the testing of 11 full-scale spliced beams are analyzed, including one beam per concrete type (except for RCA50) for investigating the top-bar effect. Experimental results are compared to six different analytical models available in literature. Results are also evaluated based on the bond database of specimens fabricated with RCA developed through literature survey as well as the database proposed by ACI Committee 408 for bond in CC. On average, SC specimens exhibited 15% higher normalized bond strength compared to the Reference beams. Performance of SC mixture was similar to that of RCA50, which were both slightly (6%) lower than that of the FA50 beams in terms of bond strength. No sign of top-bar effect was observed for the FA50 and SC beams. [ABSTRACT FROM AUTHOR]

Roller-compacted concrete (RCC) is concrete that has no slump, no forms, no reinforcing steel, no finishing, and is wet enough to support compaction by vibratory rollers. Due to the effectiveness of curing on properties and durability, the essential aim of this research is to study the effect of various curing methods (air curing, 7 days of water curing, emulsified asphalt curing, and permanent water curing) and porcelanite (lightweight aggregate used as an internal curing agent) with different replacement percentages of fine aggregate (volumetric replacement) on RCC and to explore the possibility of introducing practical RCC for road pavement with a minimum requirement of curing. Specimens were sawed from slabs of 14.96 x 14.96 x 3.94 in. (380 x 380 x 100 mm). Results show that using 5% porcelanite improved RCC (with air curing) as compared to reference RCC (with permanent water curing) by percentages ranging from 0.4 to 1.7, 3.6 to 28.9, and 15.9 to -41.3% for bulk density, flexural strength, and water absorption, respectively. [ABSTRACT FROM AUTHOR]

There is a demand for flowing concrete (FC) in concrete structures that are inaccessible and have congested reinforcement. Although mixture proportioning methods are available for conventional concrete (slump < 7 in. [178 mm]) and for self-consolidating concrete (very high slump values and high flow), until recently, a rational method for proportioning FC has not been available. There is a knowledge gap for proportioning FC mixtures (slump > 7.5 in. [190 mm]). The mixture proportioning method presented herein involves quantitatively assessing the coarse aggregate (CA) shape and packability along with the combined aggregate void (AV) content to proportion FC mixtures. The aggregate characteristics can be used to determine the fine aggregate (FA)-to-CA ratio (FA/CA) that results in a minimum aggregate void content. Using this minimum void content and the aggregate characteristics, the paste volume for flowable concrete trial mixtures can be estimated. This research determined that the past volumen (PV)-to-AV ratio (PV/AV) significantly influences the slump flow and VSI (stability) but does not significantly influence the J-ring passing ability for the mixtures assessed in this research. Results indicate that FC mixtures with adequate flowability, stability, and passing ability can be proportioned using this method. [ABSTRACT FROM AUTHOR]

High-performance concrete (HPC) mixtures were produced using 100% coarse recycled concrete aggregates (RCAs) from three different qualities. The concretes were produced using two binders: portland cement and portland cement with 30% of fly ash. Moreover, the fly ash mixtures underwent two different curing methods: conventional and steam curing. The effects of RCA on the physical, mechanical, and durability properties of HPC were studied for the production of prestressed elements. The natural aggregates could be completely replaced by RCA sourced from the same quality HPC. It was determined that when using lower-quality aggregates, the use of fly ash produced low 1-day compressive strength, with the consequent necessity to use steam curing to fulfill the standard requirements to be used in the production of prestressed elements. The steam curing had negative effects on the long-term mechanical properties; however, these effects were attenuated by using RCAs, which maintained their great durability. [ABSTRACT FROM AUTHOR]

A total of 65 concrete mixtures were made in a laboratory study to assess the direct relationship of aggregate type or chemical composition of an air-entraining agent to air void clustering in concrete. Concrete retempering was incorporated into the study because it has previously been linked to air void clustering. In addition to compressive strength testing at 7 and 28 days, an automated air void analysis, including a new method of clustering evaluation, was performed. Study results revealed that air void clustering is not responsible for decreased compressive strength of retempered concrete because neither aggregate type nor chemical composition of the air-entraining agent significantly impacted the severity of void clustering. Strength loss was found to correlate with total air and water content rather than air void clustering. [ABSTRACT FROM AUTHOR]

Fly ash is used as partial replacement of cement in concrete. The residual carbon in fly ash adsorbs some of the organic concrete admixtures, altering the concrete properties. The use of fly ash in concrete is limited by the lack of adequate fly ash adsorption capacity quantification tools. This paper presents the fly ash iodine number test for the direct measurement of the adsorption capacity of coal fly ash. This test can be used to determine suitability of fly ash for concrete. The developed test was evaluated by comparing the results obtained with the loss on ignition (LOI) and foam index test results for the same fly ash samples. Results show that the fly ash iodine number test can replace current qualitative indicators of adsorption capacity and can be directly used for the characterization and specification of fly ash for the use in concrete. [ABSTRACT FROM AUTHOR]

This paper presents a method for determining the supplementary admixture content in fresh concrete mixtures based on their dielectric properties obtained with ground-penetrating radar (GPR). The amplitudes of the electromagnetic pulses generated by the GPR before and after traveling through the fresh concrete mixture are measured and have been correlated to the replacing proportion of portland cement (PC) with the supplementary admixture (fly ash [FA], ground-granulated blast-furnace slag [GGBFS], silica fume [SF], or metakaolin [MK]) in the mixture. A linear relationship between the amplitude change of the reflected electromagnetic pulse and the supplementary admixture content in the fresh concrete mixture is observed, based on which a theoretical model is established. The effects of temperature, water-binder ratio (w/b), and high-range water-reducing admixture on the amplitude change are also investigated. [ABSTRACT FROM AUTHOR]

To evaluate measures to prevent alkali-silica reaction (ASR) in concrete and to correlate short-term laboratory tests to longterm performance, an outdoor exposure site was established in Kingston, ON, Canada, in 1991. Alkali-silica reactive aggregate was combined into six concrete mixtures using various cements and supplementary cementitious materials (SCMs). Both unreinforced and reinforced 0.6 x 0.6 x 2 m (24 x 24 x 79 in.) beams, and 0.2 x 1.2 x 4 m (8 x 48 x 158 in.) pavement slabs were instrumented and have been monitored for 20 years. The high-alkali cement concrete cracked at 5 years and low-alkali cement cracked after 12 years. The high-alkali cement was replaced with various amounts of SCMs. Two concretes, containing 50% ground-granulated blastfurnace slag (GGBFS) and a ternary blend of 25% slag plus 3.8% silica fume interground with a high-alkali portland cement, have neither expanded nor cracked. After 14 years, cores were examined petrographically, chloride penetration profiles were made, and chloride diffusion as well as rapid chloride permeability tests, were performed. [ABSTRACT FROM AUTHOR]

This paper describes a new concept for reducing early-age shrinkage in hydrating cement-based materials. The concept consists of adding a partially hydrated cementitious material (PHCM) as a concrete admixture. The added PHCM stimulates the formation of a hydrated cement paste structure and provides microcrystals of hydration products, which act as passive internal restraining clusters within the fresh concrete. The passive restraining system thus developed resists bulk deformations, leading to lower shrinkage. In this paper, the concept of a self-restraining shrinkage system is proposed and discussed, and its effect is examined experimentally including compressive strength, setting time, heat of hydration, autogenous shrinkage, thermal analysis, nuclear magnetic resonance, and scanning electron microscope (SEM) micrograph analysis. Experimental results indicate a high potential for producing self-restraining shrinkage concrete. In particular, using concrete returned to batch plants and intended for disposal as a PHCM, with sufficient precautions to maintain the quality of concrete, can yield significant economical and environmental benefits. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the difference between using manufactured or waste-expanded polystyrene (EPS) as an aggregate replacement in concrete. Concrete mixture proportions are held constant, whereas two types of EPS--reground waste material (RGD) and manufactured spherical bead (BD)--replace a portion of the fine aggregate. The plastic state and hardened state properties are quantified and compared between test batches. The plastic state measures of consistency, air content, and unit weight are reported. The measured hardened state properties include compressive strength, elastic modulus, strength-weight ratio, and energy-related toughness as determined using compression load-deflection curves. The results indicate that, for comparable concrete mixtures, BD mixtures exhibited improved workability and reduced air entrapment or entrained air as compared to RGD mixtures due to differences in EPS particle surface characteristics. Furthermore, statistically significant increases in compressive strength and energy-related toughness are demonstrated for BD mixtures in comparison to RGD mixtures. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation of using phase-change materials (PCMs) in portland cement concrete. The objective of this study is to improve the thermal properties of concrete as a structural material. A compression test, flexural test, drying shrinkage test and thermal conductivity test were conducted. PCMs are used in concrete mixtures as both sand replacement and additives. The results revealed that in the replacement method, the loss of compressive strength due to the addition of PCM is not as high as the additive method. For up to 20% sand replacement by PCM, the strength loss is not significant for structural applications. The specific heat of the concrete increased considerably. Thus, the thermal conductivity of the concrete is reduced and the insulation capacity of the concrete is improved. A flexural test, drying shrinkage test, and microstructure analysis provide a good understanding of the PCM-modified concrete. Overall, the results show that it is quite promising to use PCM in concrete to improve its insulation capacity with decreased thermal conductivity and, at the same time, that it is possible to keep the strength loss of the concrete in an acceptable range. [ABSTRACT FROM AUTHOR]

This paper addresses the permeation properties of self-consolidating concretes (SCCs) with different types and amounts of mineral admixtures. Portland cement (PC), metakaolin (MK), fly ash (FA), and ground-granulated blast-furnace slag (GGBFS) were used in binary, ternary, and quaternary cementitious blends to improve the durability characteristics of SCCs. For this, a total of 22 SCCs were designed that have a constant water-binder ratio (w/b) of 0.32 and a cementitious materials content of 926.75 lb/yd3 (550 kg/m3). In addition to compressive strength and ultrasonic pulse velocity, the permeation resistance of SCCs was determined by means of chloride ion permeability, water permeability, and sorptivity tests. The test results indicated that the permeation properties of SCCs appeared to be very dependent on the type and amount of the mineral admixture used; the SCC mixtures containing MK were found to have considerably higher permeability resistance than the control mixture. [ABSTRACT FROM AUTHOR]

Self-consolidating concrete (SCC) is a recently developed innovative construction material. No additional compacting is needed because of its high filling ability; consequently, the labor cost of compacting is economical. SCC, however, needs a stronger formwork that can resist the higher lateral pressure of cases that use ordinary concrete. This study uses the proposed two-function model to: 1) characterize the pressure response of a fresh SCC mixture; and 2) evaluate the maximum pressure that develops on the formwork. Various SCC compositions were experimented with to show the validity of the evaluation. The experimental results and analytical interpretation suggest that the maximum lateral pressure allowed in the design of the SCC formwork could be determined from two parameters that depend on the placement rate and the duration of the placement. [ABSTRACT FROM AUTHOR]

Autogenous shrinkage, significant primarily in concretes with a low water-cementitious material ratio (w/cm), has received more attention in recent years due to the increasing use of high-performance concretes (HPCs). In this study, autogenous shrinkage was quantified in both unrestrained and restrained concrete. The specimens were sealed and kept at a constant isothermal temperature of 20°C (68°F) to prevent deformation due to temperature change or moisture loss. Various materials were evaluated to compare their effectiveness in reducing autogenous deformation and stress development, including saturated lightweight aggregates, shrinkage-reducing admixtures (SRAs), and a shrinkage-compensating additive (based on calcium sulfoaluminate). The data obtained also provide insight into the mechanisms behind autogenous shrinkage and the resulting stress development in restrained members and quantify the effects of methods used to reduce autogenous shrinkage and the resultant stresses. [ABSTRACT FROM AUTHOR]

The article presents a study which analyzes the dynamic segregation of self-consolidating concrete (SCC). It states that segregation utilizes a large quantity of high-range water-reducing admixture to attain high flow and passing capacities. It mentions the use of the visual stability index in ASTM C1611/C1611M to the study the segregation. Results show the influence of paste rheological and aggregate properties, velocity of the concrete and the force in the flowing surface.

The article discusses the method used on the evaluation of concretes containing pozzolanic materials under the rapid chloride penetration test (RCPT). Benchmarking was used to evaluate the presence of fly ash, granulated blast-furnace slag and the silica fume as additives in the production of concrete. The RCPT was then applied over the air-stored and water-cured specimens within 90 days. A statistical experimental design method was also used to determine the values of the chosen variables, such as the binder content, pozzolanic material content and water-binder ratio (w/b). A total of 80 mixtures were obtained and tested under the curing condition. Moreover, it was evaluated that pozzolanic material content substantiates more than (w/b) on chloride permeability for water-cured concretes.

The article provides information on a research about the fundamental aspects that result from using mineral admixtures in high-performance concrete (HPC). It focuses on the impact of various pozzolanic admixtures on the process of pore network refinement. It states that HPC is known for the refinement of its capillaries' pores, which induces two opposite phenomena such as improved mechanical performances and self-dessication shrinkage due to high capillary depression. It discusses cement hydration reaction from solid products and a pore system. The study used mercury intrusion porosimetry (MIP) to determine the porosity and pore size distribution of concrete. Results show that refinement of the capillary network and evolution with time are linked with mineral addition type and fineness.

The article provides information on a research that investigates the rheological properties of fresh concrete that incorporates different chemical admixtures as a function of the mixing time, admixture dosage, and temperature. It states that three chemical admixtures were used in the study such as polycarboxylate-, melamine sulfonate-, and naphthalene sulfonate-based water reducing admixtures. It also discusses the process of continuous mixing of concrete incorporating chemical admixtures. Results show that the fresh concrete mixtures demonstrate progressive stiffening with time and temperature. Moreover, it concludes that the study serves as a tool to control concrete production in hot weather environments.

The article discusses the use of leftover household paint to manufacture concrete, investigating the effect of waste latex paint (WLP) on the fresh and mechanical properties of concrete. Such properties, the authors state, include air content, slump and slump loss, plastic density, setting time, as well as compressive and flexural strength. Also detailed is a test program which analyzed the WLP-modified concrete for durability related to rapid freezing-and-thawing cycles and chloride ion penetration.

The article evaluates the impact of thixotropy-enhancing agent (TEA) on the variations in thixotropy and formwork lateral pressure of self-consolidating concrete with slump flow consistency. The study involves the testing of six mixtures containing various TEA concentrations along with either a melamine- or polycarboxylate-based high-range water-reducing admixture. Results indicated that the use of TEA can significantly increase the degree of thixotropy and reduce the framework pressure compared with similar mixtures containing conventional viscosity-enhancing admixtures.

The article presents an investigation which aims to develop a laboratory device to describe the formwork pressure behavior of self-consolidating concrete. The device reduced the cost and time needed to conduct the same research on real structures. The effects of casting rate and mixture composition were studied by pressurizing a volume of material inside a cylinder and recording the lateral pressure evolution. Results showed that framework pressures less than hydrostatic are achievable while higher pressures were associated with higher water-binder ratios and casting rates. It was found that incorporation of fly ash reduces self-consolidating concrete formwork pressure.

The article discusses how the evaporation of water causes the formation of concave menisci on the surface of fresh concrete. It also studies the development of plastic shrinkage cracks in mortars that contain a commercially available shrinkage-reducing admixture (SRA). Research findings indicate that less evaporation, reduced settlement and less capillary tension result from the lower surface tension of the pore fluid in the mortars with SRA.

The article reports the efficiency of fly ash in mitigating alkali-silica reaction (ASR). Data from previous studies were used to evaluate the effectiveness of fly ashes in avoiding ASR based on their chemical composition. Moreover chemical index was used to characterize the chemical constituents of fly ash and cements as well as to evaluate the efficiency of ashes that did not meet either specifications.

The article describes an experiment which evaluated the flow properties of fluid concrete using a tube viscometer. Eight workable concrete mixtures were proportioned with varying high-range water-reducing admixture dosage and cement-to-aggregate and fines contents. The viscometer was found to be capable of measuring adequate flow curves. It could be a reliable tool for quality control in concrete production.

Examines the performance of supplementary cementitious materials in concrete resistivity and corrosion monitoring evaluations. Effect of cementitious materials on concrete durability; Comparison of the performance of cementitious materials; Resistivity values.

Conducts a study to produce an economical self-consolidating concrete (SCC) with desired properties using viscosity modifying admixtures (VMA). Presentation of the comparative performance of SCC manufactured with fly ash (FA), slag cement and VMA based on cost and mechanical properties; Focus on the performance of 21 concrete mixtures; Possibility of getting a cheap SCC through FA, slag cement and VMA integration.

The author comments on a paper by Pania Meshgin et al on the effect of phase-change materials (PCM) on some properties of concrete. The author believes that the claim of the paper that the w/c was kept constant for both the PCM replacement and PCM additive methods appears to be false since the PCM was in the form of wet cake having 30% water, so the moisture that comes from the PCM should be accounted for.