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A predictive chloride permeability model accounting for the concrete mixture and cement hydration is developed. This paper presents the formulation, calibration, evaluation and validation of the proposed model. An experimental program is developed to evaluate the model. Analysis of the results reveal that the model provides a good fit to the experimental data and does not contain outliers or discerning pattern. Furthermore, the model is validated using an extensive database from the literature to test its accuracy and generalization capability. The corresponding standard error and correlation coefficient are 182 Coulombs and 0.90, respectively. Accordingly, the proposed model can be utilized in the design of concrete mixtures to ensure that chloride permeability requirements are met and improve the sustainability of concrete structures.

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It has been proven by various studies that adding silica fume (SF) alone or nano-silica (NS) alone can provide significant beneficial effects on the durability of concrete. In theory, SF and NS may also be added together, but up to now, such possible combined usage of SF and NS for improving the durability of concrete, especially the sulphate and chloride resistance, has not been deeply explored. In this paper, the individual and synergistic roles of SF and NS in the sulphate and chloride resistance of concrete were investigated by producing a series of concrete mixes containing varying SF, NS and water contents for strength test, sulphate attack test and rapid chloride permeability test. It was found that the combined addition of SF and NS can further enhance the sulphate and chloride resistance to higher than possible with the single addition of SF or NS. From the experimental results, the cementing efficiencies of SF and NS were evaluated, from which it was revealed that there exist certain synergistic effects offered by the combined addition of SF and NS on the sulphate and chloride resistance.

Chloride diffusion coefficients, which include the chloride diffusion coefficient D RCM measured from the rapid chloride migration (RCM) test, the instantaneous chloride diffusion coefficient D ins and the apparent chloride diffusion coefficient D a determined by the chloride natural diffusion test, are the important indexes for the chloride permeability of concrete. D a denotes the average diffusion coefficient over the whole exposure period. Both D RCM and D ins essentially represent the instantaneous diffusion coefficient, which reflect the influence of real-time changing environmental factors on the chloride permeability of concrete. In this paper, the method for determining the time-dependent model of D ins was firstly studied based on Fick’s second law. Subsequently, the time-dependent models of D ins and D RCM were respectively established through the chloride natural diffusion test under artificial simulation marine environment and the RCM test. According to the comparative analysis of D ins and D RCM , the RCM modified factor f ( t ) was proposed to quantify the relationship between D RCM ( t ) and D ins ( t ), and the modified model of D RCM was established. Finally, the suggested modified model of D RCM was applied to predict the chloride concentrations in concrete, which was verified by experimental results. Results showed that the values of D ins and D RCM were identical at the initial exposure time, while D RCM gradually came to be larger than D ins with the increasing of exposure time. The main reason for the difference between D ins and D RCM is that the process of chloride diffusion in concrete is influenced by convection and chloride binding during the chloride natural diffusion test, which can be ignored in the RCM test.

The chloride profile in carbonated concretes with fly ash were measured after rapid chloride permeability test, so as to investigate the influence of carbonation degree on chloride ions diffusion and distribution. It is found that fly ash improved the carbonation resistance of concrete with low water-to-binder ratios while reduced that with high water-to-binder ratios. The capacities of binding chloride and chloride penetration resistance were enhanced in the early stage of carbonation. However, both abilities were significantly reduced in the late carbonation stage. Moreover, in the late but not completely carbonated stage, a peak appeared in the chloride concentration profile.

Carbonation treatment was recently developed to enhance the properties of recycle concrete aggregate and prepared concrete, but the durability of concrete with carbonated recycled aggregate have received little consideration in the previous studies. This study investigates the chloride permeability and the resulting steel corrosion of concrete with carbonated recycled fine and coarse aggregates, and the effects of recycled aggregate quality on chloride permeability are presented. The carbonization treatment was first applied to recycled aggregate to prepare carbonated recycled aggregate; then, the chloride permeability and steel corrosion experiments were conducted on concrete with carbonated recycled aggregate. The results exhibit that carbonation treatment improves the physical performance of recycled aggregate, which results in an increase in the compressive strength of preparing recycled concrete. Concrete with carbonated recycled aggregate has a lower chloride permeability than that with non-carbonated recycled aggregate, and the improvement in the chloride permeability resistance is more obvious for concrete with carbonated recycled fine and coarse aggregates. In particular, the improvement of chloride permeability resistance becomes more distinct with the reduction of recycled aggregate quality. The addition of carbonated recycled aggregate reduces the steel corrosion risk of reinforced recycled aggregate concrete, and the chloride permeability and steel corrosion risk follow a linear trend.

Properties of ultra-high performance concrete (UHPC) which used ground granite powder (GGP) to replace cement by different ratios (from 0 to 25%) are experimentally investigated. The hydration products and pore structure on the micro scale, and the compressive and flexural strength as well as chloride permeability on the macro scale, were studied. Influence of curing conditions, i.e., standard curing (SC), warm water curing (WWC), and autoclaved curing (AC), was also explored. It was found that though the replacement of cement by GGP did not influence the morphology and chemical compositions of hydration products, however, the pore structure changed significantly over the replacement ratio, i.e., ωGGP. Compared to SC and WWC, AC can significantly improve the hydration degree of cement and promote the polymerization degree of hydration products. WWC and AC also improved the pore structure of UHPC prepared with GGP. Compressive and flexural strength as well as the anti-permeability were found to first increase and then decrease with the growth of ωGGP; the optimal ωGGP were 5%, 10%, and 15% for UHPC specimens cured under SC, WWC, and AC, respectively. It was also found that the compressive and flexural strength are linearly related to the total porosity, while the chloride permeability is linearly related to the contents of harmful and more-harmful pores.

The objective of this study was to determine the utilization potential of Spray Dryer Absorber Material (SDAM) as an additive in concrete made with portland cement. Utilizing SDAM for beneficial use such as portland cement replacement reduces the CO2 impact for every cubic meter of concrete placed, and provides a means for utilities to avoid the impacts of landfilling. The utilization of SDAM in concrete is often avoided due to delay in setting time, i.e. early-age strength-gain, and expansion related durability issues. The study included SDAM collected from five different coal combustion utilities. A series of laboratory experiments were conducted on the fresh and hardened concrete made by replacing 20 wt% of the portland cement. The findings of this research demonstrates that despite slow strength gain at early ages, a 20 wt% replacement of portland cement yielded a concrete that met the desirable 28-day performance criteria. Additionally, the incorporation of SDAM containing elevated levels of fly ash content improved the resistance to chloride permeability, and autoclave expansion resistance of concrete. These results provide evidence against the stigma of poor durability when using SDAM in concrete.

The durability of concrete cast near the conventional formwork (steel or wood) is reduced because of higher water-cement (w/c) ratio as compared with the concrete present in the core of the member. Various controlled permeability formwork (CPF) liners absorb or drain out excess water near formwork, can reduce the increase in w/c ratio of concrete near the formwork. This paper presents a quantitative study showing improvement in the properties of near surface concrete (NSC) by the use of a commercially available CPF liner, and comparing the performance of more easily available and cheaper alternatives to CPF liner used. Two types of concrete mixes with identical w/c ratio but different water contents were used. Three specimens were made for each of the two types of concrete mix and one surface for each of the specimen was cast using one of the CPF liners among a commercially manufactured CPF, particle board, and gunny bag. Four tests: Rapid chloride permeability test, AgNO3 colorimetry test, initial surface absorption test and pull off test were performed to study durability properties of NSC. Study of physical appearance in terms of blowholes and grey area on the concrete surface using image processing is also presented in the paper. Though commercially manufactured CPF produces better surface than the particle board and gunny bag, the improvement in NSC properties by use of gunny bag is also noteworthy.

This article presents the effects of basalt-polypropylene fibers on the compressive strength and chloride ion resistance of concrete with matrix strength grades C30, C40, and C50. Test results indi...

Coal Bottom Ash (CBA) is the waste material produced by coal-based power plants, particularly in Malaysia around 1.7 million tons of CBA was produced annually, which is major environmental concern. Therefore, the use of CBA as a partial replacement of cement in concrete is a possible solution for that pollution; this approach also creates a new corridor in the field of concrete production. However, this study aims to evaluate the effects of CBA as cementitious material on the concrete properties. This study incorporated 10% CBA as a cement replacement by weight method in concrete. However, concrete samples were prepared with and without CBA and immersed in water for 7, 28, 56 and 90 days. Next, the performances of concrete with and without CBA were evaluated in terms of workability, compressive strength, and rapid chloride permeability test. It was found that due to presence of CBA in concrete, workability reduces; no substantial growth in compressive strength at the early ages but substantial rise in strength was noticed after 56 days. Almost 4.7% higher strength was recorded than the control specimens at 90 days. Besides that, concrete containing CBA has lower chloride penetration as compared to the control specimen, which shows its better durability performance. It can be concluded that CBA has an enormous potential to be utilized as a cementitious material in durable concrete production.

This paper presents the long-term durability performance of semi-lightweight concrete containing various levels of supplementary cementing materials (SCM) and steel fibers when exposed to a harsh marine environment for up to 25 years. Concrete specimens (305 × 305 × 915 mm [1 × 1 × 3 ft.]) were casting using W/CM in the range of 0.26 to 0.60. The depth of chloride penetration was greater than 90 mm (3.5 in.) for all the control specimens (without fly ash and silica fume). However, mixes containing both silica fume and fly ash (with W/CM ranging from 0.40 to 0.60) performed very well resulting in chloride penetration of approximately 40 mm (1.6 in.) during the same period. The results from the chloride permeability testing also indicate significant increases in the resistance to chloride-ion penetration for ternary concrete containing fly ash and silica fume.

An experimental study on the durability of thermal insulation concrete with recycled aggregates (RATIC) subjected to the combined action of chloride salt erosion with 3.5% NaCl solution and freeze-thaw cycles (referred to as salty F-T cycles) has been carried out. In this study, the volume of the natural coarse aggregates has been replaced by recycled coarse aggregates (RCA) at replacement rates of 0%, 30%, 50%, 70%, and 100%. The results show that thermal insulation aggregate glazed hollow beads (GHBs) had a positive effect on the durability of concrete and RCA had an enormous negative influence on the durability of RATIC exposed to the salty F-T cycles. After 100 salty F-T cycles, the relative dynamic modulus of the elasticity of samples with RCA was below 60% compared to at the start of the F-T cycles. RCA has a significant effect on the chloride permeability of RATIC compared to natural aggregates. This phenomenon was caused by the special multi-interfaces structure of RATIC that are the result of the old interfacial translation zones (ITZs). These aggravate frost damage and negatively affect the durability of concrete in the salty F-T cycles environment.

Concrete containing reactive MgO can obtain superior mechanical properties to conventional concrete when subjected to accelerated carbonation curing. This study aims to evaluate the influence of r-MgO replacement levels and accelerated carbonation (CO2 concentration of 99%) curing on the mechanical properties and rapid chloride permeability of concrete containing reactive MgO. Concrete cylinders with r-MgO replacement levels of 10%, 30%, 50% 70% and 90% were studied. Experimental results reveal that carbonation curing improves the mechanical properties of reactive MgO concrete compared to uncarbonated specimens, especially during the first three days of carbonation exposure. Influence of accelerated carbonation on concrete specimens with different r-MgO replacement levels, yields the formation of carbonation products, which diminishes the pore volume and affects the rapid chloride permeability. The rapid chloride permeability of concrete is influenced by the decreases in the overall porosity, the conductivity of pore solution and the connectivity of pore structure due to carbonation.

Portland cement concrete and fly ash concrete were subjected to the ASTM C1202 rapid chloride permeability test (RCPT). When the RCPT was complete, the chloride profiles of the specimens were determined by collecting concrete powder samples at controlling depths. Based on Faraday's laws of electrolysis, the mass of electrolysis deposition is directly proportional to the quantity of electricity (coulombs). This study showed a same phenomenon that a linear relationship was found between the charge passed during the RCPT and the total amount of chloride obtained from the chloride profile. The total amount of chloride in the specimen can be determined by measuring the 6 h charge passed from RCPT. The chloride profile can be obtained based on the measurement of charge passed and the surface chloride content. After the completion of the RCPT, additional step taken during the modified RCPT procedure entails measuring the surface chloride content. Based on the chloride penetration depth obtained from the chloride profile, a modified RCPT method was used to compute the chloride migration coefficient and assess the chloride permeability of concrete.

This paper presents the results of an experimental study of chloride permeability in alkali-activated fly ash, alkali-activated slag, and Portland cement concrete. Test methods include the rapid chloride permeability test (RCPT), AC and DC electrical resistivity, and the 90-day salt ponding test. We hypothesize that differences in pore solution chemistry between alkali-activated and Portland cement binders render electrical methods unable to accurately estimate chloride permeability in alkali-activated concrete. The present study seeks to evaluate this hypothesis by comparing results from electrical tests with diffusion coefficients from salt ponding tests. Contrary to previous claims, the RCPT provided a good estimate of chloride permeability in both alkali-activated slag and alkali-activated fly ash concrete. RCPT results showed excellent correlation with diffusion coefficients determined from salt ponding tests. Resistivity-measurements exhibited poor correlation to diffusion coefficients and overestimated the resistance to chloride ion penetration. Furthermore, AC and DC resistivity measurements showed significant disagreement for alkali-activated concrete. Finally, evidence form salt ponding tests suggests differences in chloride binding potential between alkali-activated and Portland cement concretes.

Palm oil fuel ash (POFA) is an agro-waste byproduct disposed as landfills without being recycled. Ground POFA is a suitable supplementary cementitious material that can be utilized in different types of concrete. However, problems associated with the reduction of workability and early-age compressive strength of concrete, as well as limited replacement levels of POFA, have been encountered. Heat treatment of ground POFA (T-POFA) can effectively enhance the performance of POFA and reduce its limitations. However, the energy consumed during such heat treatment is high. Moreover, limited original POFA (approximately 30%) can be used to prepare T-POFA. In this study, a new method was introduced to prepare treated POFA, called modified treated POFA (MT-POFA) with full usage of original POFA. MT-POFA was then used as a cement replacement at 0%, 30%, 50%, and 70% to produce sustainable self-compacting concrete. Test results showed that the fresh properties of all concretes containing MT-POFA were ranged within SCC requirements. The mechanical properties exhibited a reduction in the early ages of MT-POFA concretes; however, with increased curing time, these properties were significantly improved. SCC incorporating MT-POFA exhibited significant resistance against rapid chloride permeability test and elevated temperature, and performed better than the control SCC. In general, MT-POFA exhibited significant potential use as a cement replacement in self-compacting concrete.

This paper presents the durability performance of concrete incorporating high-volumes of fly ash exposed to a harsh marine environment for 19 to 24 years. Concrete specimens (305 × 305 × 915 mm [1 × 1 × 3 ft.]) were cast using W/CM in the range of 0.31 to 0.46, various types of fly ash with replacement levels of 56 or 58%, and various types of normal density and lightweight aggregates. Surface erosion/scaling was seen on all specimens; the extent of erosion was slightly worse for fly ash concrete with normal density aggregate compared to the controls (without fly ash), but fly ash concrete with two of the three lightweight aggregates exhibited severe surface erosion. Laboratory testing included taking cores from each block and determining the existing chloride profile, compressive strength and “chloride permeability” (ASTM C1202). The depth of chloride penetration was found to be in excess of 100-mm (4 in.) for the concrete specimens without fly ash, whereas the presence of fly ash significantly decreased the depth of penetration to approximately 30 and 40 mm in specimens containing either normal density or lightweight aggregate, respectively. The increased penetration in the concrete with lightweight aggregates is attributed to the surface erosion observed with these concretes. The results from the chloride permeability testing also indicate significant increases in the resistance to chloride-ion penetration for fly ash concrete.

Influence of nanosilica and sugar cane bagasse ash (SCBA) on the mechanical and durability properties of mortar, is investigated in this study. Sixteen mortar mixtures were designed with a particular water to binder ratio of 0.485 and a sand to binder ratio of 2.75. Test specimens were prepared with 3% and 6% replacement of cement weight with nanosilica and a 10–30% replacement of cement weight with SCBA. A compressive strength test was applied to evaluate the mechanical performance of mortars containing nanosilica and SCBA. In addition, transport tests, chloride permeability, electrical resistivity and mercury intrusion porosimetry of single, binary, and ternary blended mortars were conducted to investigate the influence of replacement materials on durability properties of mortars. Nanosilica improved mechanical and durability properties of mortar, while SCBA did not have a substantial influence on mortar performance according to lower strength and durability at early ages. The addition of SCBA in mixtures containing nanosilica intensely decreased compressive strength at the ages of 3 days and 7 days. However, ternary mixture results showed the best performance in the long term.

Most of the states in our country have banned sand quarrying from the river beds, causing a scarcity of natural river sand for the construction sector. Manufacture sand (M-sand) is one of the alternate solutions to replace the river sand (R-sand) in concrete. The main aim of the present study is to evaluate the durability parameters of concrete with M-sand when compared to that of concrete with R-sand. Corrosion of reinforcement is one of the main deteriorating mechanisms of reinforced concrete due to the ingress of chloride ions or carbon-di-oxide. For comparative evaluation of durability parameters, accelerated tests such as Rapid Chloride Permeability Test, Rapid Chloride Migration Test and accelerated carbonation test were carried out on specimens of R-sand and M-sand. All tests were carried out after 90 days of casting. Test results reveal that the durability parameters of the concrete with M-sand in chloride induced environment is relatively better than that of concrete with R-sand and hence is recommended to use M-sand as a replacement to R-sand.

The paper presents the properties of low-calcium fly ash based geopolymer concrete in which fly ash was partially replaced (0, 10, 20 and 30%) with ordinary Portland cement (OPC). Tests were conducted for workability, compressive strength, split tensile strength and rapid chloride permeability (RCPT) up to the age 28 days. SEM, EDS and XRD analysis were also carried out. Test results indicate that workability of low-calcium fly ash based geopolymer concrete decreased with increase in OPC content. Further, inclusion of OPC enhanced the compressive strength and reduced the permeability at all ages (3, 7 and 28 days). However optimum results were obtained for geopolymers with 20% OPC. SEM, EDS and XRD analysis confirmed the modifications in matrix making it denser, compact and less permeable.

This study investigated the effects of nano rice husk ash (NRHA) and micro rice husk ash (MRHA) on chloride permeability, electrical resistivity, capillary absorption and compressive strength of mortars. It was found that the incorporation of NRHA and MRHA enhanced mortar performance in the long term, whereas NRHA contributed to considerable enhancements at both early and long-term ages. Results proved that the strength and durability properties of mortars containing NRHA up to 7.5% levels of replacement by weight of cement gradually enhanced in comparison with control mix. However, mortars incorporating 2.5% NRHA together with 12.5% MRHA demonstrated the best improvements for durability and strength development at the age of 90 days.

Durability characteristics of self-compacting concrete (SCC) made with iron slag (IS) are presented in this paper. For this purpose, initially, a control SCC was designed, and then fine aggregates were partly (0, 10, 25 and 40%) replaced with iron slag. Various tests were done for fresh SCC properties, compressive strength and durability properties such as rapid chloride permeability, water absorption, resistance to sulphate attack and ultra-sonic pulse velocity up to the age of 365 days. SEM and XRD analysis was also carried out. The test result shows that SCC incorporating iron slag gives better strength and durability than control mixture of SCC, and can be suitably used in SCC.

Chloride diffusion coefficient depends on many variables including concrete quality, environmental conditions, and time. In this investigation, the concrete quality and time were studied while maintaining the environmental conditions constant. Fifty-three concrete mixtures were tested based on a refined statistical analysis. Enhanced response surface method (RSM) was used to present the most significant factors affecting the chloride diffusion at different ages. The tested mixtures contained various water-to-binder (W/B) (ratios 0.3–0.5), metakaolin (MK) replacement (0–25%), and total binder content (350–600 kg/m 3 ). Bulk diffusion test was adopted for two years to determine the time-dependent coefficient m of chloride diffusion for all mixtures based on the error function solution to Fick's law. This coefficient was calculated based on two different bulk diffusion test methods: total and average methods. Design charts were developed to facilitate the optimization of mixture proportions for designers/engineers. The investigation also included some experimental relationships between the rapid chloride permeability test (RCPT), chloride diffusion coefficient, and compressive strength results. The results showed that the values of the chloride diffusion indicated a general reduction from 28 days to 760 days of testing. As the percentage of MK or binder content increased or as the W/B ratio decrease, the chloride diffusion reduction coefficients, m total and m avr , were found to increase. Based on the analysis of variance (ANOVA) from the statistical model, MK was found to be the most significant factor affecting the chloride diffusion at late ages (360 and 720 days), while the W/B ratio was the most significant factor affecting early ages of chloride diffusion (28 and 90 days). The developed models and design charts in this paper can be of special interest to designers/engineers by aiding prediction of service life of concrete containing MK.

This paper presents new models to predict chloride penetration into self-compacting concrete (SCC) using the rapid chloride penetration test (RCPT). The research mainly focuses on the effect of supplementary cementitious material (i.e., fly ash and silica fume) and elevated temperature curing of SCC on results of the RCPT. Models are developed to predict the value of RCPT using two statistical algorithms, namely Multivariate Adaptive Regression Spline (MARS) and Minimax Probability Machine Regression (MPMR). Both models incorporate the combined effect of fly ash, silica fume and elevated temperature curing on the RCPT, and a comparative study between the models is also discussed. The analysis confirms that both MARS and MPMR are promising models for the prediction of RCPT results.

A rapid chloride migration test (RCM) was used to measure the chloride diffusion coefficient of cement-based materials. A semi-empirical formula for chloride diffusion coefficient including water-cement ratio and curing age parameters was developed, which can be used to predict the variation of the chloride diffusion coefficient in the later stage. Finally, using the COMSOL finite element software and the parameters obtained in the experiment, the chloride diffusion process of the sample was simulated. The penetration depths of chloride ions at different water-cement ratios were obtained, and they were in good agreement with the experimental values, with deviations less than 10%. Through the simulation, we can clearly see that the concentration distribution of chloride ions and the depth of penetration depth decrease with increasing water-cement ratio, and increase with age.

For structural health monitoring, electrical resistivity measurement (ERM) method is commonly employed for the detection of concrete's durability, as indicated by the chloride permeability and the corrosion of steel reinforcement. However, according to previous experimental studies, ERM results are susceptible to significant uncertainties due to multiple influencing factors such as concrete water/cement ratio and structure curing environment as well as their complex interrelationships. The present study therefore proposes an XGBoost algorithm-based prediction model which considers all potential influential factors simultaneously. A database containing 800 experimental instances composed of 16 input attributes is constructed according to existing reported studies and utilized for training and testing the XGBoost model. Statistical scores (RMSE, MAE and R2) and the GridsearchCV feature are applied to evaluate and optimize the established model respectively. Results show that the proposed XGBoost model achieves satisfactory predictive performance as demonstrated by high coefficients of regression fitting lines (0.991 and 0.943) and comparatively low RMSE values (4.6 and 11.3 kΩ·cm) for both training and testing sets respectively. The analyses of the attribute importance ranking also reveal that curing age and cement content have the greatest influence on ERM results.

The mechanical properties, microstructure and permeability of high-volume iron tailing powder (HVITP) concrete and high-volume fly ash (HVFA) concrete were comparatively investigated by measuring the adiabatic temperature rise, rate of temperature rise, compressive strength, splitting tensile strength and chloride permeability grade of concrete and determining the pore structure, bound water content and morphology of paste. The total adiabatic temperature rise of HVITP concrete are lower than that of HVFA concrete. But the early higher rate of temperature rise of HVITP concrete is obtained. The HVITP concrete shows low compressive strength and splitting tensile strength, coarse pore structure, loose microstructure and high chloride permeability compared with HVFA concrete with the same water/binder ratio. The early temperature matching curing (TMC) adversely affects the later-age properties development of HVITP concrete, but it promotes the properties development of HVFA concrete. The decrease in water/binder ratio or the partial replacement of ITP with slag improves the properties of HVITP concrete, especially for the early properties under TMC condition. But these two means still lead to properties difference between HVITP concrete and HVFA concrete due to the low reactivity of ITP.

Chloride penetration frequently leads to a steel corrosion and reduces the durability of reinforced concrete. Although the previous studies have investigated the chloride permeability of recycled aggregates concrete (RAC), the chloride permeability of RAC with pre-damage received little considerations. Considering that the RAC may be subjected to various exposure environments, this paper focused on exploring the chloride permeability of RAC under the coupling effect of freezing-thawing, elevated temperature or mechanical damage. The freezing-thawing, elevated temperature or applied loading test was first employed to induce initial damage on RAC, and then the chloride diffusivity test was conducted on RAC with various pre-damages. The findings showed that the chloride permeability of RAC increased with increasing recycled coarse aggregate (RCA) content. Exposing to harsh environment, the incorporation of RCA increased the freezing-thawing, elevated temperature or mechanical damage of RAC. The chloride permeability increased with increased initial damage, and a good relation could be observed between them. The incorporation of RCA improved the sensitivity to the chloride permeability of RAC exposed to harsh environment; such as, the chloride diffusion coefficient of RAC with 100% RCA was 51.4% higher than that of the plain concrete without pre-damage, while the results were 233.3% and 62.1% after 75 freezing-thawing cycles and 80% fc.

A vast amount of CO2 is released in the cement production and its application. Numerous researches are paying close attention to replacing cement with any natural and/or recyclable components to reduce the waste emissions and protect the environment. Fly ash (FA) and coal gangue (CG), as supplementary cementitious materials, can be used as a replacement of cement in order to prepare green concrete. In this research, an indoor experimental study was conducted to explore the mechanical properties and chloride permeability of concrete incorporating fly ash and coal gangue and to evaluate their application possibility. The cement replacement level was set at 10%, 20%, 30%. Each replacement level consisted of 7 different mass ratios of fly ash to coal gangue including 100/0, 80/20, 60/40, 50/50, 40/60, 20/80 and 0/100. Furthermore, the effect of different fineness (200 mesh, 325 mesh, 500 mesh, 1250 mesh, 2000 mesh) of coal gangue on the mechanical properties, frost resistance and chloride ion penetration resistance of concrete was studied. Results of this study indicated that the optimal replacement level of 20% for green concrete with the mass ratio of fly ash to coal gangue at 40/60 resulted in 4.5% and 5% improvement in mechanical performance and chloride penetration resistance, respectively. Also, 2000 mesh was recommended as the optimal fineness of coal gangue in comprehensive consideration of mechanical performance, chloride penetration and frost resistance.

This study investigates the autogenous self-healing capability of one-year-old engineered cementitious composites (ECC) with different mineral admixtures to understand whether self-healing performance in late ages is similar to that of early ages. Sound and severely pre-cracked specimens were subjected to different environmental conditions including water, air, "CO2-water," and "CO2-air" for one year plus 90 days of initial curing. Self-healing performance of ECC mixtures was assessed in terms of crack characteristics, electrical impedance testing, rapid chloride permeability testing and microstructural analysis. Laboratory findings showed that the presence of water is crucial for enhanced autogenous self-healing effectiveness, regardless of mixture composition. "CO2-water" curing resulted in the best self-healing performance of all curing conditions, which was confirmed with results from different performance tests throughout the experimental study. By further curing specimens under "CO2-water" (depending on the ECC mixture composition), cracks as wide as half a millimeter (458 mu m) were easily closed by autogenous self-healing within only 30 days of further curing, and all cracks closed completely after 90 days. Because high levels of CO2 emission are a global problem, the effectiveness of "CO2-water" curing in closing microcracks of aged cementitious composites specimens through autogenous self-healing can help reduce the increasing pace of CO2 release. The results of this study clearly suggest that late-age autogenous self-healing rates of ECC specimens can be significantly enhanced with proper further environmental conditioning and mixture design. (C) 2018 Elsevier Ltd. All rights reserved.

Massive concrete structures tend to have high cracking risk due to early temperature rise. High-volume mineral admixture concrete, which has low hydration heat, is suitable for massive concrete structures. In this paper, the properties of high-volume fly ash (HVFA) concrete and high-volume steel slag (HVSS) concrete were compared under two different curing conditions (standard curing condition and temperature match curing condition). The results show that the promoting effect of temperature match curing on the early strength of HVFA concrete is more obvious than that on HVSS concrete. Temperature match curing has negative effect on the late strength and elastic modulus of HVSS concrete. The promotion of temperature match curing to the elastic modulus development is not so obvious as that to the strength development. Temperature match curing can significantly decrease the chloride permeability of HVFA concrete, but its influence on the chloride permeability of HVSS concrete is inconspicuous. Though the adiabatic temperature rise of HVSS concrete is lower than that of HVFA concrete, which is beneficial to its application to the massive concrete structures, its strength especially the splitting tensile strength and resistance to chloride ion penetration need to be improved.

In this study, the influence of nanosilica hydrosols and rice husk ash (RHA) on the compressive strength, chloride permeability, electrical resistivity and capillary absorption of single and binary blended mortars was investigated. Results showed that the incorporation of nanosilica improved mortar performance, while RHA did not have a significant influence and mainly attributed to lower strength and durability at early ages. It was found that the addition of RHA in mixes containing nanosilica, dramatically decreased compressive strength at ages of 3 and 7 days. However, binary mixtures displayed the best results for strength development and durability at ages of 28 and 90 days.

Microcracking has been suspected of influencing the transport properties and durability of concrete structures, but the nature and extent of this influence is unclear. This paper focuses on the influence of drying-induced microcracking. Samples were prepared with sample thickness/maximum aggregate size (t/MSA) ratios ranging from 2 to 20 and dried to equilibrium at 105 °C or 50 °C/7% RH or 21 °C (stepwise: 93% RH → 55% RH) prior to characterisation of microcracks and transport tests. Results show for the first time that there is a significant size effect on microcracks and transport properties. Samples with smaller t/MSA had more severe microcracking and higher gas permeability. Gas permeability decreased with increasing t/MSA (for a decreasing MSA), and remained constant beyond t/MSA of 10. However, this size effect was not seen on gas diffusivity and sorptivity. The implications of these findings particularly regarding the influence of drying-induced microcracks on the durability of concrete structures are discussed.

In this study, the influence of nanosilica hydrosols with specific surface areas of 100 m 2 /g, 200 m 2 /g and 300 m 2 /g and silica fume with specific surface area of 21 m 2 /g on chloride permeability and electrical resistivity of concrete is investigated. The results indicate that the nanosilicas, especially at higher replacement levels, enhanced the chloride and electrical resistance of concrete at early ages, while silica fume did not have a significant influence on these characteristics at early ages. The results also show that the nanosilicas with lower surface areas had better performance in enhancing the chloride and electrical resistance of concretes compared to the finer ones, especially at 28 days and 90 days. Silica fume achieved a similar performance to the best performing nanosilica at 28 days and surpassed it at 90 days.

In this paper, the durability properties of self-compacting concrete (SCC) containing rice husk ash (RHA), metakaolin (MK) and a combination of MK and RHA (1:1 ratio) were evaluated and their relationships discussed. The durability properties of the various mixtures were studied. The results showed that SCC blended with RHA and a combination of RHA and MK showed a considerable improvement in durability than unblended SCC (100% OPC). However, the performance of SCC blended with MK was unsatisfactory in an acid environment. In addition, it was found that resistance to acid attack was directly related to the silica ratio (SR).

In this paper, effect of steam and water curing on the compressive strength development and transport properties such as water sorptivity, rapid chloride ion permeability, and gas permeability of concretes containing various volumes of lightweight fly ash aggregate (LWA) were investigated. In production of concrete, a fixed amount of lightweight coarse (LWCA) aggregate plus varying amounts of lightweight fine aggregate (LWFA) were used. Utilization of LWFA was achieved by volumetric substitution of fine aggregate with five different replacement levels namely, 0%, 25%, 50%, 75%, and 100%. Therefore, five different concrete mixtures were produced for this experimental study. The produced concretes were divided into two parts one of which was initially steam cured while the other was directly exposed to water curing. After initial steam curing regime, the steam cured (SC) concretes were also transferred to water until testing Mechanical properties of concretes were monitored through compressive strength development over 56 days, while transport properties were measured by means of water sorptivity, gas permeability and rapid chloride permeability tests conducted at 28 and 56 days. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.

A concrete surface was treated by in situ synthesised super-absorbent resin (SAR) of poly(acrylic acid-co-acrylamide). Experiments aimed at determining the resistance to carbonation and the chloride permeability of SAR-treated concrete compared with control concrete specimens were conducted. The corrosion risk and corrosion rate for the rebar embedded in SAR-treated and control concrete specimens at various periods of carbonation were evaluated through the accelerated corrosion test, wherein the rebar was subjected to 3·5% sodium chloride solution. The results show that the resistance to carbonation and chloride permeability of SAR-treated concrete is higher than that of control concrete, and that the corrosion risk and corrosion rate of steel embedded in SAR-treated concrete is smaller than that of steel in control concrete. Lighter carbonation can effectively decrease the chloride permeability of concrete, but serious carbonation is harmful to the long-term maintenance of the passive film of steel in concrete.

This paper presents a portion of a state highway agency pooled fund research project to develop performance criteria for concrete that will be resistant to penetration of chlorides, cycles of freezing and thawing, and sulfate attack. This paper presents the portion of the study pertaining to penetration of chlorides. To simulate standard and service conditions, specimens were subjected to either immersion or to a cyclic wetting and drying exposure in chloride solution. Measured apparent chloride diffusion coefficients, determined in accordance with American Society for Testing and Materials (ASTM) C1556, were correlated with results of rapid index test methods that provide an indication of the transport characteristics of concrete. Rapid index test methods included were rapid chloride permeability, rapid migration, conductivity, absorption, and initial and secondary sorptivity. A set of rapid index test methods and specification criteria that can reliably classify mixtures based on their resistance to chloride ion penetration are proposed.

Rapid chloride permeability test (RCPT) is one of the widely used test methods to rapidly assess the durability of concrete, specifically its resistance against chloride ion penetrability. Many researchers have questioned the applicability of RCPT in mixes having supplementary cementitious materials (SCMs). The present work analyses the performance of RCPT in concretes that contain different dosages of three SCMs such as slag, Class F fly ash and Class C fly ash. In addition to the conventional measurements of current at half an hour interval, other details of the tests such as initial current, temperature development during the experiment, and depth of chloride ion penetration are also measured. Good correlations are obtained between total charge passed and other additional measurements such as initial current, depth of chloride ion penetration, temperature reached during the experiment etc., which are reported by other researchers with mixes having only OPC as binder. Furthermore, the results of RCPT are well correlated with the results of Wenner 4-probe surface resistivity test, which is free from many of the criticisms of RCPT. The paper concludes that RCPT can be used as a reliable accelerated test method to assess chloride ion penetrability in concretes that have supplementary cementitious materials such as fly ash and slag.

This paper presents the results of an experimental investigation carried out to evaluate the influences of curing methods and mineral admixtures on the strength and chloride permeability of concrete. Rapid chloride ion penetration tests (ASTM C 1202) were used to measure the chloride permeability of concrete. Test results indicated that steam curing decreased the 28 days compressive strength of plain concrete by 11 %. Incorporating slag, fly ash, and silica fume can significantly mitigate this harmful consequence. After autoclave curing however, all concrete’s strength exceeds 80 MPa. Steam and autoclave curing increase the electrical charge passed through plain cement concrete by 110 and 224 %, respectively, when compared with normal curing. For steam curing, incorporating silica fume is the most efficient means to reduce the chloride permeability of concrete. For autoclave curing however, incorporating 30 % fly ash is the most efficient means to reduce chloride permeability.

Although self compacting concrete (SCC) is currently used in many countries, there is a fundamental lack of the intrinsic durability of the material itself. This article presents the outcomes from a research program on principal indicators that define the durability of SCC (sorptivity, porosity and chloride ion permeability) and compares these indicators with the corresponding parameters of conventional concrete. The results show, for the first time, that there is a correlation between the various durability indicators for the specific filler additives used in the mix designs incorporated in this paper. Such a correlation may be used to assess the durability of SCC without the need to rely on time consuming artificial weathering experimental procedures. " 37 320 325

This paper presents the results of a study conducted to evaluate the corrosion resistance of self-compacting concrete (SCC) prepared using quarry dust powder (QDP), silica fume (SF) plus QDP or fly ash (FA). SCC specimens were prepared and tested for corrosion resistance, chloride permeability and chloride diffusion. The results indicated that the time to initiation of reinforcement corrosion in M4 (8% QDP plus 5% SF and w/c = 0.4) specimens and M2 (8% QDP and w/c = 0.38) specimens was more than that in M5 (30% FA and w/c = 0.4) specimens. The corrosion current density on steel in the SCC specimens was very low in the initial stage of exposure to 5% NaCl solution and it increased with increasing period of exposure. Corrosion activation was noted on steel in M1, M3, and M5 specimens. However, it was not noted in M2 and M4 specimens even after 990 days (33 months) of exposure. The chloride permeability in SCC specimens incorporating QDP or FA was moderate and it was low in the specimens incorporating QDP plus SF. The lowest diffusion coefficient was noted in M2 specimens while it was the highest in M5 specimens.

This paper aimed to study the properties of Self-Compacting-Concrete (SCC) such as compressive strength, splitting tensile strength, rapid chloride permeability, porosity, and mass loss when exposed to elevated temperatures. In this research, mixes were prepared with three percentages of class F fly ash ranging from 30% to 50% and for comparison; one controlled mixture without fly ash was also produced. The variables included were the temperature effects (20 °C, 100 °C, 200 °C, and 300 °C) using Ordinary Portland Cement. SCC mixes developed 28 days compressive strength ranging from 21.43 to 40.68 MPa and splitting tensile strength ranging from 1.35 to 3.60 MPa. Test results clearly show that there is little improvement in compressive strength within temperature range of 200–300 °C as compared to 20–200 °C but there is little reduction in splitting tensile strength ranging from 20 to 300 °C and with the increase in percentage of fly ash.

Pore structure and chloride permeability of concrete containing nano-particles (TiO2 and SiO2) for pavement are experimentally studied and compared with that of plain concrete, concrete containing polypropylene (PP) fibers and concrete containing both nano-TiO2 and PP fibers. The test results indicate that the addition of nano-particles refines the pore structure of concrete and enhances the resistance to chloride penetration of concrete. The refined extent of pore structure and the enhanced extent of the resistance to chloride penetration of concrete are increased with the decreasing content of nano-particles. The pore structure and the resistance to chloride penetration of concrete containing nano-TiO2 are superior to that of concrete containing the same amount of nano-SiO2. However, for the concrete containing PP fibers, the pore structure is coarsened and the resistance to chloride penetration is reduced. The larger the content of PP fibers, the coarser the pore structure of concrete, and the lower the resistance to chloride penetration. For the concrete containing both nano-TiO2 and PP fibers, the pore structure is coarser and the resistance to chloride penetration is lower than that of concrete containing the same amount of PP fibers only. A hyperbolic relationship between chloride permeability and compressive strength of concrete is exhibited. There is an obvious linear relationship between chloride permeability and pore structure of concrete.

Concrete durability mainly depends on the diffusion characteristics of concrete. Chloride ion diffusion is one of the main parameters affecting the durability of Reinforced Concrete Structures. The chloride ion penetration is determined under accelerated diffusion test condition with 12 V (Norwegian method). Depending upon the concrete quality, the diffusion test duration will vary. Generally, high grade concrete will have longer test duration as compared to lower grade concrete. In this paper, OPC concrete of M30, M40, M50, M60 and M75 grades were studied for diffusion properties under different voltages 12, 20, 30, 40, 50 and 60 V. A comparative study was made with standard Rapid Chloride Permeability Test with respective voltages. It has been observed that chloride profile and diffusion coefficient were high in low grade OPC concrete and low for high grade concrete. Minimum test duration was observed at higher voltages. With the increased voltage, the chloride profile and diffusion coefficient were found to be high.