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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]

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.

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]

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]