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In order to predict the influence of fly ash (FA) and Alccofine (AL) on the compressive strength (CS), flexural strength (FS), split tensile strength (STS), and rapid chloride permeability test (RCPT) of concrete in a different age of samples, an experimental-based dataset was selected. This research was carried out by investigating the forecasting accuracy of different data mining (DM) models. To gain this, a score-based system is proposed to compare the applied method's productivity based on R, RMSE, and MAE results. As shown in the results, CS, FS, STS, and RCPT's predicted values are very close to the experimental values in both training and testing samples. By considering the highest R among the developed models, the MLP model was the most efficient algorithm, at 0.9983, 0.9981, and 0.985 to predict CS, FS, and STS, respectively. Regarding RCPT results, Additive regression algorithm has the highest accuracy with TRS at 53. According to the ranking score, for prediction all four mechanical properties of concrete modified with FA and AL, among the applied models, SMOreg has the lowest rank, and GPR could be recognized as the second-best method.

Purpose High-ductility cementitious composites (HDCC) have an excellent crack controlled capacity and corrosion resistance capacity, which has a promising application in structure engineering under harsh environment. The purpose of this study is to explore the corrosion mechanism of steel bar in HDCC. Design/methodology/approach Intact and the pre-cracked HDCC specimens under the coupled action of different dry–wet cycles and chloride attack were designed, and intact normal concrete (NC) was also considered for comparison. Corrosion behavior of a steel bar embedded in HDCC was analyzed by an electrochemical method, a chloride permeability test and X-ray computed tomography. Findings Steel corrosion probability is related to the chloride permeability of the HDCC cover, and the chloride permeability resistance of HDCC is better than that of NC. Besides, crack is the key factor affecting the corrosion of steel bars, and the HDCC with narrower cracks have a lower corrosion rate. Slight pitting occurs at the crack tips. In addition, the self-healing products and corrosion products fill up the cracks in HDCC, preventing the external aggressive ions from entering and thereby decreasing the steel corrosion rate. Originality/value HDCC has a superior corrosion resistance than that of NC, effects of variable crack width on corrosion behavior of steel bar in HDCC under the coupled actions of different dry–wet cycles and chloride attack are investigated, which can provide the guide for the design application of HDCC material in structure engineering exposed to marine environment.

In this work, two UHPC premixes were applied in investigating compressive strength and chloride permeability. Results indicated that the compressive strength of UHPC increased with content of steel fiber in standard curing. Compressive strength of type-A premix specimen with 2.0 vol% steel fiber was more than 150 MPa after heat curing. All UHPC in the experiment showed low chloride permeability under heat curing. Compared with type-B premix, the type-A premix had greater advantages in mechanical property and chloride permeability. In addition, the low porosity and dense microstructure of UHPC specimen were detected by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM), respectively. Furthermore, it was found that the introduction of fiber could refine the pore size distribution of specimen.

Now days where being expenses is increased and abundant waste material is produced by stone processing units, it is necessary to have certain knowledge where economical substitutes in concrete can resolve this issue of waste materials. Mechanical and Durability properties of concrete are studied here when sand and cement are substituted for quartzite rock dust up to 70 percent and 40 percent. Compressive and Flexural Strength test were being carried out for different concrete samples of embedded quartzite rock dust at age of 7 and 28 days. Rapid chloride permeability test (RCPT) as per ASTMC1202 were being performed on various cylindrical concrete specimens cured at 28 days. Total Charge passed value unbelievably decreased with addition of quartzite rock dust suggesting that its accumulation improve concrete durability.

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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Large amount of slag is obtained during the production of ferrochromium. This by-product has properties comparable to natural aggregates. However, almost all of the ferrochromium slag is landfilled. The main objective of this study was to investigate the effects of ferrochromium slag aggregate on the mechanical properties and permeability of concrete. For this purpose, waste ferrochromium slag was used as aggregates in normal concretes and alkali-activated mixtures, with five different water/binder ratios. Concretes with limestone and Portland cement were produced as references. Mechanical properties of the concretes were determined. Chloride permeability and resistivity tests were performed. The results indicate that the strengths of the mixtures were similar to each other for given water/binder ratios. Rapid chloride permeabilities of the mixtures were close to each other, except for high water/binder ratios. Electrical resistivities of the mixtures were recorded. A strong relationship between electrical resistivity and chloride permeability was obtained. The results confirmed that the ferrochromium slag aggregates may be successfully used in concretes ranging from low-strength to higher strength classes.

This study examined low-binder ultrahigh-performance concrete (UHPC) when nanosilica (NS) and/or microsilica (MS) were incorporated in Portland cement (PC) in either binary or ternary blends. Two groups were created for this purpose, and they were divided based on the presence or absence of silica flume (SF). NS was used as a restricted substitute for cement by weight at five different percentages (0%, 0.5%, 1%, 2% and 3%). The total binder was 800 kg/m3, and the ratio of water to binder was 1:5. Results demonstrated that optimum resistance to chloride permeability, gas permeability, sorptivity, water absorption and water penetration came from the 3% UHPC sample. The ternary blends of NS, PC and SF yielded better results than binary PC and NS blends. A 1% NS replacement gave similar effects to the UHPC properties investigated as a 10% MS replacement.

Various challenges encountered in the construction industry has led to the production of concrete, with not just high strength, but also with enhanced durability properties. Several research works have been carried out using replacement of constituent materials and introduction of various admixtures in concrete. Alccofine is one of such promising micro fine material. This study investigates the performance of hardened concrete using nano materials. Effects of alccofine (AL) and zinc oxide (ZnO) on the durability and strength of hardened concrete were explored. Series of tests were conducted by substituting cement by weight with 10% AL and adding ZnO in proportions, 0.25%, 0.5%, 0.75% and 1%. Based on the results obtained, the strength properties of concrete reduced as cement replacement level rose beyond 10%. The durability performance of the concrete, in terms of rapid chloride permeability, water permeability test, sea water attack and chloride resistance, was within acceptable limist, even as the ZnO was increased. This study has generally proposed a sustainable solution to produce durable concrete that could have useful aaplication in the construction industry.

Accompanied by high absorption and desorption capacity, Masonry Chips Aggregate (MCA) offers profound potential as a low-cost internal curing medium. This study overviews the previous studies conducted by research group of one of the authors to evaluate overall performance of concrete at various MCA replacement proportions. A considerable increase in Compressive Strength Ratio (CSR) and Tensile Strength Ratio (TSR) along with a decrease in Charge Ratio (CR) in chloride permeability tests has been observed for using MCA under improper curing conditions, particularly at 20% replacement proportion. Use of MCA has also increased Corrosion Initiation Time (CIT) values of concrete when subjected to at both improper curing conditions.

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.

In this paper, effects of natural pozzolan, called Chekneh, as a part of cement replacement and wood chips as a part of mixture aggregates on the mechanical and durability properties of concrete were studied. Nine concrete mixtures proportions within two categories were prepared. In the first category, the properties of concrete were evaluated by adding 10 and 15% of Chekneh pozzolan or wood chips and the second category containing combination of Chekneh pozzolan and wood chips was prepared. The results showed that adding optimal content of natural Chekneh, 10% of cement weight replacement to concrete improves the mechanical properties including flexural, compressive and tensile strength and durability properties of concrete including volumetric water absorption, electrical resistance and rapid chloride permeability. Also, the replacement of 10% wood chips as a part of aggregates causes improvement in mechanical properties of concrete. The combined effect of natural pozzolan and wood chips has the most positive effect on increasing the compressive, tensile and flexural strength in concrete, and the sample which contains 10% pozzolan and 10% wood chips has the most improvement compared to the control sample.

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.

High cycle fatigue behaviors (crack widths, deflections and fatigue life) and chloride permeability of RC beams were experimentally investigated. The experiment processes included initial fatigue loading followed by 3 months of NaCl solution wet-dry cycles without loading, and then fatigue life tests before chloride content measurement. The loading levels (ratio of the maximum fatigue loads over the ultimate static strength) and initial fatigue loading cycles are taken as parameters in this study. Results show that: (1) the fatigue behaviors of RC beams are greatly affected by the loading level and chloride corrosion, but they are rarely influenced by the initial fatigue loading cycles; (2) chloride content markedly increase when the loading levels exceed 0.3; (3) at the loading levels of 0.4 and 0.45, combined actions of initial fatigue damage and chloride corrosion cause at least 13% decrease of the total fatigue life; (4) initial fatigue loading cycles barely affect the residual fatigue life of RC beams when initial fatigue damage of RC beams are in the slow variation stage of damage development.

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...

The main cause of reinforced concrete deterioration is chloride attack. Chloride ions penetrated into the concrete can destroy the passive layer around steel reinforcement provided by the high alkalinity and low pH of cement paste, activating electrochemical corrosion. Durable concrete gives more corrosion resistance of embedded steel that continuously ensures a stronger long life of the reinforced concrete structure. The concrete structures within the seashore areas allow chloride ions to easily penetrate into the concrete and reduce the life span of the structure. In this paper, the rapid chloride permeability test (RCPT) as per ASTM C1202 is presented to determine the chloride profile, concrete chloride resistivity and rate of corrosion. The specimens were prepared with concrete incorporating three different type fibres including steel, E-waste copper wire and E-glass fibres of 1.0% by volume of concrete. The RCPT was conducted for time period of 28 days, 56 days and 90 days. The final RCPT results of fibre-reinforced concrete mix with control mix concrete were compared. The test result shows that the E-glass fibre-reinforced concrete was more durable than the other concrete mixes.

It is well known that aggressive environments like the sulfate attack are the major factor affecting the durability of concrete. Thus, this research was carried out to estimate the durability of rice husk ash (RHA) concrete exposed to sodium sulfate attack through wetting and drying cyclic. Five levels of cement replacement namely 0, 10, 20, 30 and 40% (by weight) were studied. After being kept in the sodium sulfate solution for 3, 7, 28, 56, 90 and 180 days, the RHA concrete specimens were evaluated based on the rapid chloride permeability and its correlation. It was found that the total charge passed in Portland cement concrete was higher than that of RHA-blended cement concrete. However, it continued to decrease along with increasing levels of RHA replacement. In addition, the use of 40% RHA in the cement resulted in better resistance to sulfate attack when the concrete specimen was exposed to the wetting and drying cycles. It can be concluded that the use of 10 to 40% RHA effectively decreased the penetration depth (charge passed) in the concrete under sulfate attack.

The goal of the current paper is to study the effect of natural pozzolana (NP) when ground to a micro and nano size on some concrete properties. Syria is rich in natural pozzolana with an estimated quantity of nearly 1 billion tonnes. Four properties, namely compressive strength, chloride permeability, chloride-induced reinforcement corrosion and acid attack on mortar, have been investigated. Six levels of micro-NP (from 0% to 50%), and nano-NP (from 0% to 5%) were added as cement replacement to produce the studied concrete/mortar mixtures. The results revealed that grinding NP to extremely fine particles has positive effects. The shortcoming related to the lower early compressive strength can be eliminated. Further, much lower chloride permeability and longer corrosion initiation times were clearly observed in the concrete containing nano-NP. The best results were obtained when NP was added at 30% or more at micro-scale and at 3–4% at nano scale. Furthermore, acid resistance particularly at the early ages of exposure was noticeably improved with such additives. SEM technique fitted with EDX analysis was employed in the current research to study the microstructure of the cement paste after being exposed to acid solutions. XRD and TGA techniques were used as well.

Environmental impact and inherit brittleness of conventional concrete can be reduced simultaneously by utilising recycled aggregates instead of natural ones and fiber-reinforcements. In this research, the effect of incorporating single steel fiber (SF) and polypropylene fibers (PPF) and hybrid SF-PPF was studied on the performance of recycled aggregate concrete (RC). Both single fibers and hybrid fibers were used at the volume fraction of 1%. Examined properties included compressive strength-fcm, flexural strength-fbm, ultrasonic pulse velocity-UPV, water absorption-WA, and rapid chloride permeability-RCP. The results revealed the use of single SF and hybrid SF-PPF in incredibly advanced the flexural performance of RC. Single SF-reinforced-RC or hybrid SF-PPF-reinforced RC showed markedly higher flexural strength than that of the conventional plain NC. The optimum compressive and flexural strength were obtained when plain NC and RC were reinforced with 0.85%SF-0.15%PPF. Flexural strength of RC reinforced with 0.85%SF-0.15%PPF was 26% higher compared to that of the plain-NC. The use of hybrid SF-PPF also reduced the water permeability capacity of RC better than the use of single SF or PPF. Hybrid fiber-reinforced RC has implications for cheaper and eco-friendly concrete than single SF-reinforced concrete.

The main focus of this study is to investigate the pozzolanic attribute of the recycled waste glass powder used as cement replacement. A coarser glass powder (

Many researches has been carried out regarding the possible reuse of the waste materials like marble and granite powder in a economical and eco-friendly manner. The use of marble and granite products waste is identified as a substitute to cement in mortar mix to an option that come up with concrete products in a cheaper cost in the construction industry. In the sustainable point of view, an experimental study is conducted on the cement mortar with the replacement ratio of 0%, 5%, 10%, 15%, 20%, 25% and 30% of marble powder and granite powder in the cement content to examine the durability properties. For this durability study, the mortar disc specimens of dimensions 80 mm × 50 mm are prepared, cured for a period of 28 days and tested for rapid chloride permeability test. The experimental results are showing that the granite powder replaced mortar is moderately better than marble powder replaced mortar. The optimum replacement is found as 5% for marble dust and 10% for granite powder, since the penetration is low based on the experimental results.

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.

A lot of buildings and structures in coastline areas facing many issues such as huge number of cracks shown on the wall structures. Moreover, this issue is affecting the aesthetic and the beauty of the buildings. Research discover that reasons behind this problem is concrete corrosion or especially corrosion of steel that causes enormous damage to the structure. This issue starts when the chloride is containing in concrete and due to formation of the oxide film. Rapid chloride permeability test according to ASTM C1202 is performed to study the behavior of different concrete mixes such as normal concrete, concrete with fly ash and concrete with Ground Granulated Blast-furnace slag(GGBFS). In this experiment when the concrete blocks are dipped into the solution, the electric current passes through it in order to determine the permeability of the material. In addition, corrosion acceleration test is performed to observe the electric current flow through the different mixes with different time intervals and days when it is merged to sodium chloride (NaCl). From the rapped chloride permeability test results, it is found that the permeability of chloride of all mixes is categorized as a moderate. From the corrosion acceleration test, it is found that all specimen of concrete containing fly ash had an attack at the first days of the test. A little rust appears on the normal concrete mix in the second week as the magnitude of electric current passing through it was not stable.

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.

The present research aimed to study the combined effects of natural pozzolana and curing on the compressive and flexural strengths of mortars; it also investigated the chloride permeability of concrete. To do that, Ordinary Portland cement (CEMI) was used and three concrete preparations were made by incorporating natural pozzolana at a rate of 10, 20 and 30% by weight of CEMI. Moreover, three curing methods were employed. The first one is a standard curing method, at temperature 20 °C, and 2 other thermo-activation methods at the temperatures of 40 °C and 70 °C, for a setting time of 4 h. The thermo-activation methods were used to accelerate the initial hydration, for the purpose of improving the strength of the prepared mortars and concretes at the early age. The results obtained indicate that, substituting natural pozzolana for CEMI with a level below 20% gives strengths comparable to those obtained with CEMI alone. The curing methods at 40 °C and 70 °C allowed increasing mortar and concrete strengths at the early age; however, it was found that the temperature of 70 °C reduces strengths, at later age. Natural pozzolana limits the penetration of chlorides. Keywords: CEMI, Pozzolana, Hydration, Strength, Temperature, Chlorides

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.

Concrete usually suffers from deterioration caused by ions and water soaking in the cracks, pores and other defects. We have prepared epoxy solution with carbonyl solvent, where the solvent and epoxy can react with amine (curing agent) to form network. The epoxy solution has remarkable wettability on concrete surface, and it can even permeate into the pores or defects in concrete. After coating with the epoxy solution, the strength of the concrete can be improved to above 9.3 MPa. Particularly, the coated concrete exhibits excellent anticorrosion performance with total charge passed in chloride permeability as low as 130 C.

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.

The objective of this paper is to experimentally study the possibility of using nanoparticles for repairing cracks and leaks generated in the well cement used in underground gas storage and acquisition. Several types of nanoparticles can be injected into the intact/distressed (aged) cement with the newly developed electro-migration method to repair wellbore leakage. The injection of nanoparticles is evaluated by the saturate-drying method, electric conductivity method, and BET method. After the injection, the decrease of chloride permeability can be captured, and nanoparticle agglomeration can be observed. In addition, the capability of extracting harmful ions from the cement is provided simultaneously during the injection of nanoparticles.

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.

The chloride permeability of concrete (UHPC) was evaluated by means of the Rapid chloride permeation test and and standard difusion test. The tests are different in the voltage applied for accelerating the transport through the concrete specimen. The permeability strongly depends on quality and curing time of the concrete.

This study investigated the influence of nanokaolin content on the behavior of cement mortar at various curing ages. The fluidity, chloride permeability, bending and compressive strength of cement mortar with various nanokaolin additives were examined. The addition of 0%, 1%, 2%, 3%, 4%, 5% and 6% nanokaolin were taken into consideration. The results showed that the addition of nanokaolin decreases the fluidity of cement mortar, and the fluidity the cement mortar decreases with the increase of nanokaolin additives. It is obtained that the addition of nanokaolin increases both the bending and compressive strength of cement mortar, and with the increase of nanokaolin additives, the bending and compressive strength of cement mortar increase. The addition of 4% nanokaolin can result in a significant low chloride permeability of cement mortar among the seven dosages. The chloride diffusion coefficient of the mortar with the addition of 4% nanokaolin was decreased by 18.93%, 12.68% and 31.05% at 7, 14 and 28 curing days, respectively.

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.

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