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Hydrated cement is one of the complex composite systems due to the presence of multi-scale phases with varying morphologies. Calcium silicate hydrate (C–S–H), which is the principal binder phase in the hydrated cement, is responsible for the stiffness, strength, and durability of Portland cement concrete. To understand the mechanical and durability behavior of concrete, it is important to investigate the interactions of hydrated cement phases with other materials at the nanoscale. In this regard, the molecular simulation of cement-based materials is an effective approach to study the properties and interactions of the cement system at the fundamental scale. Recently, many studies have been published regarding atomistic simulations to investigate the cement phases to define/explain the microscopic physical and chemical properties, thereby improving the macroscopic performance of hardened binders. The research in molecular simulation of cementitious systems involves researchers with multidisciplinary backgrounds, mainly in two areas: (1) cement chemistry, where the hydration reactions govern most of the chemical and physical properties at the atomic scale; and (2) computational materials science and engineering, where the bottom-up approach is required. The latter approach is still in its infancy, and as such, a study of the prevailing knowledge is useful, namely through an exhaustive literature review. This state-of-the-art report provides a comprehensive survey on studies that were conducted in this area and cites the important findings.

Earth materials have been used in construction as safe, healthy and environmentally sustainable. It is often challenging to develop an optimum soil mix because of the significant variations in soil properties from one soil to another. The current study analyzed the soil properties, including the grain size distribution, Atterberg limits, compaction characteristics, etc., using multilinear regression (MLR) and artificial neural networks (ANN). Data collected from previous studies (i.e., 488 cases) for stabilized (with either cement or lime) and unstabilized soils were considered and analyzed. Missing data were estimated by correlations reported in previous studies. Then, different ANNs were designed (trained and validated) using Levenberg-Marquardt (L-M) algorithms. Using the MLR, several models were developed to estimate the compressive strength of both unstabilized and stabilized soils with a Pearson Coefficient of Correlation (R2) equal to 0.2227 and 0.766, respectively. On the other hand, developed ANNs gave a higher value for R2 than MLR (with the highest value achieved at 0.9883). Thereafter, an experimental program was carried out to validate the results achieved in this study. Finally, a sensitivity analysis was carried out using the resulting networks to assess the effect of different soil properties on the unconfined compressive strength (UCS). Moreover, suitable recommendations for earth materials mixes were presented.

The paper presents an experimental study on assessment of the effect of accelerated carbonation curing (ACC) on the performance of two concrete mixtures having the same mixture proportions but different cementitious materials (plain-cement and fly-ash-blended-cement). Different sets of specimens were cast utilising both concrete mixtures and were then subjected to ACC for ten hours at a constant pressure of 414 kPa (60 psi). After exposing the specimens to ACC, they were tested for weight gain, carbonation depth, compressive and tensile strengths, modulus of elasticity, water penetration depth, rapid chloride permeability, shrinkage, SEM and XRD. ACC of the concrete specimens for ten hours resulted in a significant weight gain with less than 2 mm of carbonation depth. Both mixtures gained compressive strength above 20 MPa after ten hours of ACC. The strength increased further when ACC-treated specimens were exposed to air, with a significant increase up to seven days for plain-cement concrete and up to 28 days for fly-ash-blended-cement concrete. Compared to reference moist-cured concretes, the ACC-treated concretes were found to exhibit a slightly lower long-term strength (15% for plain-cement and 5% for fly-ash-concrete). However, the overall performance of the ACC-treated concrete mixtures was comparable with the respective moist-cured concrete mixtures.

In the reported study, the performance of some generic and proprietary inhibitors in inhibiting corrosion of reinforcing steel in cracked and uncracked silica fume cement concrete beams was evaluat...

This paper reports the results of a study conducted to investigate the effect of concrete placement temperature and curing method on the plastic shrinkage of plain and pozzolanic cement concretes. The concrete specimens were cast at a temperature of 25, 32, 38 or 45 °C and exposed to the ambient summer conditions. The specimens were cured by applying a water-based curing compound or covering with a plastic sheet. The performance of ordinary Portland (Type I) cement, fly ash (FA), very fine fly ash (VFFA), silica fume (SF), blast furnace slag (BFS) and natural pozzolan (NP) was evaluated by measuring the plastic shrinkage strain. The results indicated that the curing compound was effective in decreasing the shrinkage strain in all concretes. It was also noted that the critical temperature at which the maximum shrinkage strain occurred was 25 °C and as the concrete temperature was approaching the ambient temperature, the shrinkage strain decreased. The 28-day compressive and split tensile strength and pulse velocity were also determined to study the effect of placement temperature on these properties. These data indicated that the critical placement temperature was both 25 and 45 °C while the optimum temperature for all cementitious materials was either 32 or 38 °C.

Accelerated carbonation curing (ACC) is a new technique for curing of concrete that entails sequestering carbon dioxide (CO 2 ) gas into freshly cast concrete, resulting in the improvement of physico-mechanical properties and durability characteristics of concrete. This paper presents the results of an experimental study conducted to evaluate the effects of carbonation pressure and duration on the CO 2 uptake and evolution of strength of a concrete mixture. Concrete specimens were cured under six ACC pressures varying from 10 to 60 psi, applied for a duration of 1–10 h in a closed chamber. The effectiveness of varying ACC pressure and duration on the properties of concrete was assessed by measuring compressive strength gain, CO 2 uptake, morphology and mineralogy of concrete. It was noted that ACC at 60 psi (414 kPa) for 10 h resulted in the maximum strength gain and CO 2 uptake, leading to a post-ACC compressive strength of more than 200% of the pre-ACC strength, and a CO 2 uptake of about 11% by mass of cement. Finally, the analysis of variance of the experimental data indicated that the duration of ACC controls the concrete properties more than the pressure used for ACC.

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.

This paper reports the results of a study conducted to investigate the effect of casting temperature and curing under hot weather conditions on the compressive and tensile strength and density (evaluated by measuring pulse velocity) of plain and blended cement concretes. The concrete specimens were cast at 25, 32, 38 or 45 °C and cured outdoors by covering them with wet burlap. The optimum casting temperature for the plain and blended cement concretes was evaluated by measuring compressive and split tensile strength and pulse velocity. Further, correlations between these properties was developed. The optimum casting temperature was noted to be 32 °C for OPC and SF cement concretes while it was 38 °C for VFFA, FA, GGBFS and NP cement concretes. A good correlation was noted between the concrete casting temperature, period of curing and the concrete properties.

The exposure temperature significantly affects the diffusion of chloride ions in concrete, and, as such, it must be taken into consideration in the development of service-life prediction models for structures exposed to chloride-bearing environments. Most of the earlier studies have used cement paste to assess the effect of exposure temperature on chloride diffusion. In the reported study, chloride diffusion in Type I and fly ash (20% fly ash) cement concrete was evaluated under field and laboratory conditions. The laboratory concrete specimens were exposed to chloride solution maintained at four temperatures (22, 35, 50 and 60 °C) for 365 days. Beam specimens were exposed in the tidal zone of a marine exposure site, along the Arabian Gulf coast, for up to 10 years to study the chloride diffusion in the field specimens. The coefficient of chloride diffusion (Da) in the concrete specimens exposed to 22 or 35 ᵒC in the laboratory was less than that in the concrete specimens exposed to 50 and 60 ᵒC. The Da for Type I cement concrete specimens increased by 3.6 times as the temperature was increased from 22 to 60 ᵒC while this increase was 2.3 times for the fly ash cement concrete specimens for a similar increase in the temperature. The Da decreased with the period of exposure in the field specimens. The values of activation energy that can be used for predicting the chloride diffusion for exposure temperature within the range of 22–60 °C were developed based on the laboratory data. In addition, mathematical models were developed relating the coefficient of chloride diffusion in the field and laboratory concrete specimens. The developed models can be utilized to ascertain chloride diffusion in field specimens, utilizing the laboratory values, and hence calculate the useful service-life of structures.

Casting temperature and curing method significantly affect the properties of concrete, especially the blended cement concretes. Consequently, it is imperative to study the influence of casting temperature and curing regime on the properties of concretes. This paper reports results of a study conducted to evaluate the properties of plain and blended cement concretes prepared using very fine fly ash (VFFA), fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBFS) and natural pozzolan (NP) cast and cured under varying temperature and curing conditions. The concrete specimens were prepared under natural summer atmosphere at intital concrete temperature of 25, 32, 38 or 45 °C. The specimens were cured under laboratory conditions by water ponding and under hot weaterher conditions by covering with wet burlap or applying a curing compound. The effect of casting temperature and curing regime on the properties of the studied concretes was evaluated by measuring compressive and split tensile strength up to 180 days, pulse velocity up to 90 days and depth of water penetration after 28 days of curing. As expected, the properties of concrete specimens cured by water ponding were better than those cured by covering with wet burlap or applying a curing compound. The properties of blended cement concretes were better than those of plain cement concretes at later ages due to the pozzolanic reaction. It is postulated that the optimum casting temperature is 32 °C for OPC and SF cement concretes while it is 38 °C for VFFA, FA, GGBFS and NP cement concretes. This finding differs with the current international practice of limiting the casting temperature to 35 °C.

Dune sand is one of the predominant soils in the world, particularly in the Arabian Peninsula and North Africa. In order to use these soils in constructions, pre-treatment of sand is essential. Though the usage of cement for stabilising sand has long been the practice to achieve the required strength, it is not cost effective and its manufacturing consumes a lot of energy. Consequently, it would be noble to use industrial by-products, often considered as waste materials, such as electric arc furnace dust (EAFD), in the stabilisation of sand. This research reports the potentiality of using EAFD for improving the strength of dune sand. Specimens, mixed with 2% cement and mixed with 5, 10, 20 and 30% EAFD plus 2% cement, were evaluated using unconfined compressive strength, soaked CBR and durability tests. Results of this investigation indicated that dune sand stabilised with 20 and 30% EAFD plus 2% cement has been qualified as a construction material for sub-base in rigid and flexible pavements, res...

This paper reports the method and mechanism for improving the strength of marl and desert sand utilizing electric arc furnace dust (EAFD), an industrial by-product, in lieu of cement or lime. EAFD was used in conjunction with a small quantity (2%) of cement. The mechanical properties and durability characteristics of marl and sand mixed with 2% cement plus 5-, 10-, 20- or 30%-EAFD, by weight of the soil, were evaluated. The soil-cement-EAFD mixtures were used to determine their unconfined compressive strength (UCS), soaked California Bearing Ratio (CBR) and durability. The risk of leaching of toxic heavy metals, such as lead and cadmium, from the stabilized soils to the groundwater was also investigated. The mechanisms of stabilization of the selected soils due to the use of EAFD along with a small quantity of cement are also elucidated. The usage of 20 to 30% EAFD with 2% cement was noted to considerably improve the mechanical properties and durability of both marl and sand.

The chlorine concentration in Superpozz (SPZ) cement concrete was analyzed using a newly designed prompt gamma-ray neutron activation (PGNAA) setup utilizing a portable neutron generator. The setup, which mainly consists of a neutron source along with its moderator placed side by side with a shielded gamma-ray detector, allows determining chloride concentration in a concrete structure from one side. The setup has been tested through chlorine detection in chloride-contaminated Superpozz (SPZ) cement concrete specimens using 6.11 and 2.86±3.10 MeV chlorine prompt gamma-rays. The optimum 0.032±0.012 wt% value of Minimum Detectable Concentration (MDC) of chlorine in SPZ cement concrete measured in this study shows a successful application of a portable neutron generator in chloride analysis of concrete structure for corrosion studies.

The use of supplementary cementing materials, such as silica fume, fly ash, blast furnace slag, and natural pozzolans, has been promoted by their technical and economic advantages. However, in certain parts of the world, where these materials are not available locally, their utilization is solely based on their technical superiority. The practice in such regions is to replace part of the cement with the selected supplementary cementing materials while maintaining constant water-to-cementitious materials ratio. In such cases, the advantage of a reduction in the water requirement of certain materials is not utilized. In the reported study, fly ash, silica fume, or a highly reactive finely pulverized fly ash replaced part of the cement. The concrete mixtures were designed for a constant workability of 75–100 mm slump. The performance of ordinary Portland cement (OPC) and silica fume (SF), fly ash (FA) and very fine fly ash (VFFA) cement concretes was evaluated by measuring the compressive strength development and reduction in both compressive strength and pulse velocity after exposure to moisture and thermal variations, and sulfate ( SO 4 - = 1%, 2%, and 5%) solutions. The effect of curing regime, namely water ponding and application of a curing compound, was also evaluated. It was noted that the water requirement of FA cement concretes was less than that of OPC and SF cement concretes. Consequently, the mechanical properties and durability characteristics of the former cements were better than those of the latter cements. It was also noted that a longer curing period, prior to the application of a curing compound, is beneficial to OPC, SF, FA, and VFFA cement concretes. Curing with water tended to improve the quality of OPC, SF, FA, and VFFA cement concretes; and as the curing period increased the quality improved further.

The Prompt Gamma Neutron Activation Analysis technique was used to measure the concentration of chloride in the blast furnace slag (BFS) cement concrete to assess the possibility of reinforcement corrosion. The experimental setup was optimized using Monte Carlo calculations. The BFS concrete specimens containing 0.8–3.5 wt.% chloride were prepared and the concentration of chlorine was evaluated by determining the yield of 6.11, 6.62, 7.41, 7.79 and 8.58 MeV gamma-rays. The Minimum Detectable Concentration (MDC) of chlorine in the BFS cement concrete was estimated. The best value of MDC limit of chlorine in the BFS cement concrete was found to be 0.034 ± 0.011 and 0.038 ± 0.012 wt.% for 6.11 and 6.62 MeV prompt gamma-rays. Within the statistical uncertainty the lower bound of the measured MDC of chlorine in the BFS cement concrete meets the maximum permissible limit of 0.03 wt.% of chloride set by the American Concrete Institute.

Due to the inferior characteristics of indigenous soils in eastern Saudi Arabia, marl is being utilized to improve their properties. Marl is calcareous in nature and it is well known for its heterogeneous nature in terms of composition and properties. Moreover, it is sensitive to changes in water content and it often requires prior treatment without which a significant strength loss will occur upon water flooding. This paper presents the results of a laboratory investigation focused on the improvement of indigenous marl for its use as a road base material. Various tests were conducted to both characterize and quantify the strength and durability of the studied marl under different field-simulated conditions with and without chemical treatment (lime and cement). The improvement in strength was assessed using California Bearing Ratio (CBR), Clegg Impact Hammer (CIH) and unconfined compressive strength tests and the durability was evaluated using standard and modified durability tests. The results indicated that cement is superior to lime both in terms of strength improvement and durability requirements.

Pozzolanic materials, such as fly ash (FA), silica fume (SF), and blast furnace slag (BFS) are added to Portland cement in concrete to prevent reinforcement steel corrosion in concrete. Further preventive measure against reinforcement steel corrosion require monitoring of chloride salts concentration in concrete using non-destructive techniques, such as the prompt gamma-ray neutron activation analysis (PGNAA) technique. Due to interferences between gamma-rays from chlorine and calcium in PGNAA technique, detection limit of chlorine in concrete strongly depends upon calcium concentration in concrete. SF mainly contains silica and its addition to cement concrete reduces overall concentration of calcium in concrete. This may result in an improvement in detection limit of chlorine in SF-based concrete in PGNAA studies. Particularly for chlorine detection using 6.11 and 6.62 MeV prompt gamma-rays that strongly interfere with 6.42 MeV prompt gamma-rays from calcium. In this study, SF was added to Portland cement to prevent concrete reinforcement steel from corrosion. The chlorine concentration in SF cement concrete specimens containing 0.2–3.0 wt% chlorine was measured through yield of 1.16, 1.95, 6.11, 6.62, 7.41, 7.79, and 8.58 MeV chlorine gamma-rays using PGNAA technique. An excellent agreement was noted between the experimental yield of the prompt gamma-rays and the gamma-ray yield calculated through the Monte Carlo simulations. Further the minimum detectable concentration (MDC) of chlorine in SF cement concrete was calculated and compared with the MDC values of chlorine in plain concrete and concrete mixed with fly ash cement. The MDC of chlorine in SF-based concrete through 6.11 MeV, and 6.62 MeV chlorine gamma-rays was found to be improved as compared to those in plain concrete and concrete mixed with fly ash cement.

In this study, plain, silica fume and fly ash cement concrete specimens prepared with varying water to cementitious materials ratio and cementitious materials content were tested for compressive strength, water permeability, chloride permeability, and coefficient of chloride diffusion after 28 days of water curing. The data so developed were statistically analyzed to develop correlations between the compressive strength and the selected durability indices of concrete. Very good correlations were noted between the compressive strength and the selected durability indices, particularly chloride permeability and coefficient of chloride diffusion, irrespective of the mix design parameters. However, these correlations were observed to be dependent on the type of cement.

Preventive measures against reinforcement corrosion in concrete require increasing concrete density to prevent the diffusion of chloride ions to the steel surface. Pozzolanic materials, such as fly ash (FA), silica fume (SF), and blast furnace slag (BFS) are added to concrete to increase its density. Monitoring the chloride concentration in concrete is required to assess the chances of reinforcement corrosion. In this study, FA was added to Portland cement concrete to increase its density. Prompt gamma neutron activation analysis (PGNAA) technique was utilized to analyze the concentration of chlorine in concrete. The chlorine concentration in the FA cement concrete was evaluated by determining the yield of 1.16, 1.95, 6.11, 6.62, 7.41, 7.79, and 8.58 MeV gamma-rays of chlorine from the FA concrete specimen containing 0.4–3.5 wt% chlorine. An excellent agreement was noted between the experimental yield of the prompt gamma-rays and the calculated yield obtained through the Monte Carlo simulations. The Minimum Detectable Concentration (MDC) of chlorine in FA cement concrete was also calculated. The best value of MDC limit of chlorine in the FA cement concrete was found to be 0.022±0.007 and 0.038±0.017 wt% for 1.16 and 6.11 MeV prompt gamma-rays, respectively. Within the statistical uncertainty, the lower bound of MDC meets the maximum permissible limit of 0.03 wt% of chlorine in concrete set by American Concrete Institute Committee 318.

Blast furnace slag (BFS) is added to Portland cement concrete to increase its durability, particularly its corrosion resistance. Monitoring the concentration of BFS in concrete for quality control purposes is desired. In this study, the concentration of BFS in concrete was measured by utilizing an accelerator-based prompt gamma-ray neutron activation analysis (PGNAA) setup. The optimum size of the BFS cement concrete specimen that produces the maximum intensity of gamma rays at the detector location was calculated through Monte Carlo simulations. The simulation results were experimentally validated through the gamma-ray yield measurement from BFS cement concrete specimens having different radii. The concentration of BFS in the cement concrete specimens was assessed through calcium and silicon gammaray yield measurement from cement concrete specimens containing 5 to 80 wt% BFS. The yield of calcium gamma rays decreases with increasing BFS concentration in concrete while the yield of silicon gamma rays incr...

This paper reports results of a study conducted to assess the properties of cement kiln dust (CKD) blended cement concretes. Cement concrete specimens were prepared with 0%, 5%, 10%, and 15% CKD, replacing ASTM C 150 Type I and Type V. The mechanical properties of CKD concrete specimens were evaluated by measuring compressive strength and drying shrinkage while the durability characteristics were assessed by evaluating chloride permeability and electrical resistivity. The compressive strength of concrete specimens decreased with the quantity of CKD. However, there was no significant difference in the compressive strength of 0 and 5% CKD cement concretes. A similar trend was noted in the drying shrinkage strain. The chloride permeability increased and the electrical resistivity decreased due to the incorporation of CKD. The performance of concrete with 5% CKD was almost similar to that of concrete without CKD. Therefore, it is suggested to limit the amount of CKD in concrete to 5% since the chloride permeability and electrical resistivity data indicated that the chances of reinforcement corrosion would increase with 10% and 15% CKD.

Large quantity of dust, commonly known as cement kiln dust (CKD), is produced during the production of Portland cement. In order to meet environmental requirements, CKD is disposed off in land fills. Recently, there has been a trend of utilizing it for soil stabilization, treatment of sewage, etc. Also, attempts were made at using it in cement products. This paper reviews the work conducted on the latter aspect and reports results of tests conducted by the authors to investigate the properties of cement-CKD combination. Results indicate that CKD does not adversely affect the properties of cement mortar. However, the implication of high chloride concentration and alkalinity of CKD on concrete durability needs to be studied.

With the advancement in cement technology, it is now possible to produce concrete of high strength with increased water/cement ratio. While this may satisfy the strength requirement, it is possible that the durability of such concrete is despaired. Though international organizations specify minimum cementititous materials content and maximum water/cementititous materials ratio, the quality assessment parameter is still the compressive strength. There is, however, a need to switch to permeability or chloride diffusion indices to ascertain the quality concrete. At the same time, compliance criteria for the present-day concrete need to be developed. In the reported study, an extensive experimental work was carried out to assess the compressive strength development, depth of water penetration and chloride permeability of plain, silica fume and fly ash cement concretes prepared with varying mixture proportions. The experimental data were utilized to develop statistical relationship between the mixture design parameters and the strength and durability indices. These data were also utilized to develop quality compliance criteria for concrete prepared with the crushed limestone aggregates.

Supplementary cementing materials (SCMs) are widely used these days to improve the durability of concrete. Silica fume has gained world wide acceptance due to its high pozzolanic reactivity compared to other SCMs. While silica fume cement concrete has several advantages over other blended cement concretes its main draw back is increased plastic and drying shrinkage, particularly under hot weather conditions. This paper reports results of a study conducted to assess these properties of plain and silica fume cement concrete specimens cast and cured in the field under hot weather conditions. The effect of specimen size and method of curing on plastic and drying shrinkage and some of the mechanical properties of silica fume and plain cement concrete specimens were evaluated. Results indicated that the type of cement significantly affected both the plastic and drying shrinkage of concrete in that these values in the silica fume cement concrete specimens were more than those in the plain cement concrete specimens. As expected, the shrinkage strains in both the plain and silica fume cement concrete specimens cured by continuous water-ponding were less than that in similar concrete specimens cured by covering them with wet burlap. The results point to the importance of selecting a good quality silica fume and good curing for avoiding cracking of concrete due to plastic and drying shrinkage, particularly under hot weather conditions.

Non-destructive evaluation of concrete is an important task of quality control in building construction industry. The quality evaluation of concrete samples was carried out using prompt gamma ray activation analysis (PGNAA) technique. In this study calcium and silicon contents of six concrete samples were determined through yield of 1.94 MeV gamma-rays from calcium and 3.54 MeV gamma-rays from silicon. The concrete samples were prepared by mixing cement, coarse and fine aggregates in different proportions. A linear correlation has been observed between the experimental yield of the prompt gamma rays and the actual calcium and silicon concentration in the concrete samples. Results of this study have demonstrated successful use of an accelerator-based PGNAA setup in non-destructive analysis of the concrete samples.

Many construction and post-construction problems have been reported in the literature when sabkha soils have been used without an understanding of their abnormal behavior, especially their inferior loading capability in their natural conditions. The strength of these soils can be further significantly decreased if the sabkha is soaked. The main objective of this study was to upgrade the load-carrying capacity of pavements constructed on sabkha soils using geotextiles, and to assess the effect of geotextile grade, base thickness, loading type (static and dynamic) and moisture condition (as-molded and soaked) on the performance of soil-fabric-aggregate (SFA) systems. In addition, the sabkha soil was treated with different dosages (5%, 7%, and 10%) of Portland cement and the performance of cement-stabilized sabkha was compared to that of the SFA system under different testing conditions. The ANOVA results indicated that the use of geotextile has a beneficial effect on sabkha soils, especially under wet conditions. Although the improvement in the load-carrying capacity of sabkha samples with high dosages of cement showed better results than the inclusion of geotextile, an economic analysis showed that the use of geotextiles would be superior. Moreover, mechanistic analysis was used to develop a prediction model for the percentage increase in the modulus of resilience.

This paper reports results of a study conducted to evaluate the effect of silica fume on the compressive strength and split tensile strength and modulus of elasticity of low quality coarse aggregate concrete. Concrete specimens were prepared with four types of low quality aggregates, namely calcareous, dolomitic and quartzitic limestone and steel slag. Results indicate that the type of coarse aggregate influenced the compressive strength and split tensile strength and modulus of elasticity of both plain and silica fume cement concretes. Both the compressive and split tensile strengths of steel-slag aggregate concrete were more than those of limestone aggregate concretes. Incorporation of silica fume enhanced the compressive strength and split tensile strength of all concretes, especially that of the low quality limestone aggregates.

The intensity of prompt gamma-ray was measured at various depths from chlorine-contaminated silica fume (SF) concrete slab concrete specimens using portable neutron generator-based prompt gamma-ray setup. The intensity of 6.11 MeV chloride gamma-rays was measured from the chloride contaminated slab at distance of 15.25, 20.25, 25.25, 30.25 and 35.25 cm from neutron target in a SF cement concrete slab specimens. Due to attenuation of thermal neutron flux and emitted gamma-ray intensity in SF cement concrete at various depths, the measured intensity of chlorine gamma-rays decreases non-linearly with increasing depth in concrete. A good agreement was noted between the experimental results and the results of Monte Carlo simulation. This study has provided useful experimental data for evaluating the chloride contamination in the SF concrete utilizing gamma-ray attenuation method.

Sabkha soils are known for their low-bearing strength in their natural condition. Moreover, the collapse potential of sabkhas presents an unacceptable risk in normal practice and calls for the improvement of their mechanical properties prior to any construction. A review of the literature indicates that research on the stabilization of sabkha is scanty despite the extensive distribution of sabkha soils worldwide. Moreover, since the sabkha is a highly variable material, there is a need to formulate a “data bank” by stabilizing as many sabkhas as possible. In this study, a “selected” sabkha soil from Al-Qurayyah, eastern Saudi Arabia, was researched for improving its properties using cement and lime at five different dosages ranging from 0 to 10%. The load-bearing capability of plain and chemically stabilized sabkha mixtures was evaluated using the CBR, unconfined compressive strength, and Clegg impact value at different moisture contents. The results indicated that cement improved the performance of stabi...

This paper reports results of a study conducted to evaluate plastic shrinkage cracking of concrete made with varying dosages of several pozzolanic materials, such as fly ash (20, 30 and 40%), silica fume (5, 10 and 15%) and blastfurnace slag (50, 60 and 70%). These concrete specimens were exposed to hot—humid and hot—dry environments. The effect of these environmental conditions on plastic shrinkage cracking was evaluated. The rate of water evaporation in the blended cement concrete specimens was noted to be more than that in the plain cement concrete specimens. Further, bleeding in the blended cement concrete specimens was less than that in plain cement concrete specimens. The cumulative effect of these two parameters resulted in increased plastic shrinkage cracking of the blended cement concretes. Although cracks were observed earlier in the plain cement concrete specimens than in the blended cement concrete specimens, the total area of cracks in the latter cements was more than that in the former cements. The results of this study also indicate that relative humidity influences plastic shrinkage cracking of concrete significantly in comparison with the effect of the type of cement.

The formation of depressions and settlement in roads shortly after being constructed is one of the major challenges facing the road authorities in the Arabian Gulf States. Such problems have been closely related to the nature of pavement materials and loading conditions as well as to the proximity of groundwater tables to the surface. A major road in eastern Saudi Arabia was reported for frequent deterioration even when the construction was properly carried out. A preliminary investigation was conducted to quantify the properties of the base course material (i.e. marl soil) and the cause of failure. The laboratory investigation indicated that the marl used in the construction, similar to other marls, has acute water sensitivity and loss of strength whenever the soil is inundated. A precautionary and immediate solution was proposed to stabilize the soil with cement. Consequently, a comprehensive laboratory program was carried out to assess the performance of cement-stabilized marl mixtures under different exposure conditions. Based on the laboratory results and the traffic data for the road under investigation, four sections were constructed, two of them being without any additive while in the other two the base course being treated with 4% cement. Continuous monitoring and evaluation of the four sections for 4 years indicated that the cement-treated road sections have exhibited superior performance over the untreated ones. Unlike the untreated sections, which have experienced various forms of deterioration within a few months after construction, the stabilized sections are still in an excellent condition.

Factorial experimental design was adopted in this investigation to assess the combined effects of the following factors on workability and compressive strength: (a) water to cement ratio (W/C), (b) total aggregate to cement ratio (TA/C), (c) fine to total aggregate ratio (FA/TA), and (d) hot-weather conditions in terms of concrete mixture temperature at placement and curing conditions. The experimental data was thereafter subjected to regression analysis to develop reliable models for predicting workability in terms of the slump and compressive strength of a concrete mixture. Results of this study indicate that lowering the concrete mixture temperature at placement alone, as recommended in the codes of practice, does not eliminate the adverse effect of hot weather on compressive strength.

This study was conducted to evaluate the effect of holidays and damage to fusion bonded epoxy coating (FBEC) on reinforcement corrosion in chloride-contaminated concrete. The effect of these parameters on the corrosion of FBEC bars was compared with corrosion of mild steel by measuring the corrosion potentials and corrosion current density at regular intervals. The corrosion current density measurements indicated that the defect-free FBEC bars were in a passive condition in the concrete specimens with up to 2% chloride by weight of cement. The long-term maintenance-free performance was not assured in the concrete specimens with chloride concentration of 1% and above and made with FBEC bars having >1% surface damage or with 3 holidays per linear foot. The long-term performance of FBEC bars with up to two pinholes (ASTM A 775 limit) was satisfactory in the concrete specimens with up to 2% chlorides, by weight of cement. Furthermore, surface damage to FBE coating is more critical compared to holidays, from the point of view of corrosion of FBEC bars, in chloride-bearing concrete.

Single prompt gamma ray energy has been evaluated to measure chlorine concentration in fly ash (FA), Super-Pozz (SPZ) and blast furnace slag (BFS) cement concrete specimens using a portable neutron generator-based Prompt Gamma Neutron Activation (PGNAA) setup. The gamma ray yield data from chloride concentration measurement in FA, SPZ and BFS cement concretes for 2.86-3.10, 5.72 and 6.11MeV chlorine gamma rays were analyzed to identify a gamma ray with common slope (gamma ray yield/Cl conc. wt%) for the FA, BFS and SPZ cement concretes. The gamma ray yield data for FA and SPZ cement concretes with varying chloride concentration were measured previously using a portable neutron generator-based PGNAA setup. In the current study, new data have been measured for chlorine detection in the BFS cement concrete using a portable neutron generator-based PGNAA setup for 2.86-3.10, 5.72, and 6.11MeV chlorine gamma rays. The minimum detection limit of chlorine in BFS cement concrete (MDC) was found to be 0.034±0.010, 0.032±0.010, 0.033±0.010 for 2.86-3.10, 5.72 and 6.11MeV gamma ray, respectively. The new BFS cement concrete data, along with the previous measurements for FA and SPZ cement concretes, have been utilized to identify a gamma ray with a common slope to analyze the Cl concentration in all of these blended cement concretes. It has been observed that the 6.11MeV chlorine gamma ray has a common slope of 5295±265 gamma rays/wt % Cl concentration for the portable neutron generator-based PGNAA setup. The minimum detectable concentration (MDC) of chlorine in blended cement concrete was measured to be 0.033±0.010wt % for the portable neutron generator-based PGNAA. Thus, the 6.11MeV chlorine gamma ray can be used for chlorine analysis of blended cement concretes.

This paper reports results of an investigation carried out to evaluate corrosion of reinforcing steel in plain and blended cement mortar specimens placed in a sabkha soil. These specimens placed at a sabkha site in the Eastern Province were retrieved at periodic intervals and the degree of reinforcement corrosion was evaluated by conducting weight loss measurements. The specimens were also analyzed to determine water-soluble chloride, and hydroxyl ion concentrations. Laboratory studies were also carried out to evaluate the time to initiation of corrosion. For this purpose, reinforced concrete specimens were exposed to a simulated-sabkha environment for a period of more than two years. The reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. Results indicate lower reinforcement corrosion activity on steel in blended cement specimens, particularly in silica fume cement specimens, than on steel in plain cement specimens, placed both in me field and in the simulated- sabkha solution.

This paper describes the results of an investigation on the effect of five stabilizing agents, namely limestone dust, marl, emulsified asphalt, cement and lime, on the properties of an arid, saline sabkha soil from eastern Saudi Arabia. Standard compaction and unconfined compressive strength tests were performed, the latter on wrapped specimens that had been allowed to cure for seven days. The results indicated that the density of sabkha mixtures could not be used as a primary criterion in any stabilization programme and the maximum strength of sabkha mixtures was attained at moisture contents much lower than the optimum. Despite the sabkha9s coarsegrained nature, neither addition of marl nor of emulsified asphalt gave any significant improvement in the properties of sabkha and the effect of adding limestone dust was marginal. However, the addition of either lime or cement in the range of 2.5 to 100y weight of soil increased the strength between and 22 times.

A review of the literature indicates that research on the durability of reinforced concrete in sulphaterich environments has primarily been confined to studies on sulphate attack. Despite the small number of reports on the effect of sulphate ions on corrosion of reinforcing steel in concrete, the findings of these reports are controversial and inconclusive. Therefore, this investigation was conducted to assess the performance of 15 reinforced concrete mixtures in a mixed magnesium-sodium sulphate environment. These mixtures comprised a combination of three Portland cements, three mineral admixtures and two water-to-binder ratios. Deterioration of concrete due to sulphate attack and corrosion of reinforcing steel was evaluated by assessing the weight loss of concrete and measuring corrosion potentials and polarization resistance at periodic intervals. The results of this investigation indicated that plain cement concretes, irrespective of their C 3 A content, performed fairly well in terms of sulphate resistance; however, they failed to protect the rebars from corrosion. Blended cement concretes, particularly those made with fly ash and blast-furnace slag, exhibited an advanced degree of deterioration due to both sulphate attack and reinforcement corrosion. Despite its inferior performance in terms of sulphate resistance, silica fume cement concrete displayed the best performance with regard to corrosion protection. A reduction in the water-to-binder ratio was generally detrimental in terms of sulphate attack in plain and blended cement concretes.

The electrochemical behaviour of reinforcing steel in plain and blended cement concrete specimens placed in sulphate, chloride and sulphate-chloride environments was investigated. The effect of cement composition and the exposure condition on the corrosion behaviour of reinforcing steel was evaluated by measuring corrosion potentials at periodic intervals and conducting potentio-dynamic scans after two and half years of exposure. The corrosion potential data indicated passive corrosion in plain and blended cement concrete specimens placed in the pure sulphate environment. The time to initiation of reinforcement corrosion, however, was higher in blended cements than plain cements in all chloride and chloride-sulphate environments. The concomitant presence of suphate and chloride salts did not significantly influence the time to corrosion initiation. The corrosion rate, however, was significantly influenced by the quantum of sulphate ions associated with the chloride salts. The superior performance of silica fume blended cement, in terms of longer time to corrosion initiation and lower corrosion rate, indicates its potential in enhancing the useful service life of reinforced concrete structures placed in the chloride-sulphate environments.

The deterioration of concrete due to sulfate salts in soils, groundwater and marine environments is a well-known phenomenon. While it is known that the use of low-C3A cements can provide protection against sulfate attack, the combined effect of chloride and sulfate salts on such a deterioration is highly debated and inconclusive. Moreover, the use of blended cements incorporating supplementary cementing materials, such as natural pozzolan, fly ash, blast furnace slag and silica fume, is becoming common these days. The performance of these cements in environments characterized by the conjoint presence of chlorides and sulfates, however, is not well documented. In this investigation, the effect of sulfate and sulfate-chloride environments on the expansion and reduction in strength of mortar specimens due to sulfate attack was evaluated. Results indicated that the presence of chloride ions in the sulfate environments mitigated the sulfate attack in plain and blended cements. The performance of plain cements was better than that of all blended cements. However, the performance of blended cements was observed to depend on the type of mineral admixture used, both in the sulfate and the sulfate-chloride environments.

This investigation was carried out to elucidate the role of chloride ions in sulphate attack in plain and blended cements. Paste and mortar specimens made with Type I and Type I cements as well as with Type I cement blended with fly ash, silica fume and blastfurnace slag (BFS) were exposed to four sulphate and/or chloride environments for a period of two years. The performance of these cements was evaluated through visual inspection and measurement of reduction in compressive strength. X-ray diffraction and scanning electron microscopic techniques were used to study the sulphate attack mechanisms in plain and blended cements in both the presence and the absence of chloride ions. Results indicate that sulphate deterioration in plain cements was mitigated by the presence of chloride ions, whereas in blended cements, particularly those made with silica fume and BFS, the beneficial effect of chloride was only marginal. This is attributed to the Mg-oriented sulphate attack which was more operative in blended cements. In contrast to the gypsum and ettringite-oriented sulphate attacks, this type of attack was not inhibited in the presence of chloride ions.

This investigation is carried out: (1) To study the effect of magnesium‐sodium sulfate environment on the performance of two plain and three blended cements; and (2) to elucidate the sulfate attack mechanisms on these cements in the mixed magnesium and sodium sulfate environment. After two years of exposure, deterioration is observed in all cements. However, the deterioration is more pronounced in blast‐furnace‐slag (BFS) and silica‐fume (SF) cements. Deterioration in these cements significantly exceeds that observed in plain and fly‐ash‐(FA‐) blended cements. XRD and SEM analyses indicate that the greater deterioration in BFS‐ and SF‐blended cements may be attributable to the depletion of the hydrated calcium hydroxide as a result of pozzolanic reaction. In the absence of Ca(OH)2, magnesium ions react more directly and extensively with the cementitious calcium silicate hydrate to generate gypsum and noncementitious magnesium silicate hydrate resulting in aggravated deterioration.