علی اکبر رمضانیان پور

Considering the successful usage of alkali activated mortars in several countries and limited research on the durability of these materials, in this paper, permeability and durability of alkali activated slag and pumice mortar in chloride environments have been studied. In order to investigate the mechanical properties and permeability of alkali activated slag and pumice mortars tests such as workability, compressive strength, capillary water absorption, water absorption, chloride ion penetration in the Persian Gulf environment and mercury intrusion porosimetry have been conducted.The results show that the compressive strength of alkali activated slag mortar containing potassium hydroxide was slightly higher than the compressive strength of samples containing sodium hydroxide. In addition, the use of 10% pumice instead of slag has increased the compressive strength of alkali activated slag mortar. Also, the 91-day compressive strength of alkali activated mortars cured in the water was 48.4% higher than those cured in the air. In general, the diffusion coefficient of chloride ions in alkali activated slag mortars was lower than the diffusion coefficient of chloride ions in Portland cement mortar, which was due to less porosity in alkali activated slag mortars and the denser structure. Also, alkali activated mortars containing 90% of slag and 10% of pumice had the lowest diffusion coefficient of chloride ions and Portland cement mortar showed the highest one, which was well matched with the result of capillary water absorption coefficient.

Previous researches have shown that due to its good adhesion, alkali-activated materials can be used as a protective overlay for concrete structures. However, the mechanical properties and durability of alkali-activated materials are not fully investigated. In this paper, compressive strength, bond strength, water penetration and half-cell corrosion potential of alkali-activated slag and pumice mortars as concrete overlay are investigated. The results show that the performance of alkali-activated slag mortar is better than Portland cement one in above tests and the use of potassium hydroxide as activator and a mixture of 90% slag and 10% pumice as based material result in the highest compressive strength and bond strength and the lowest water permeability and half-cell corrosion potential. The initial half-cell potential reading of alkali-activated mortar specimens was an average of 1.9 times more than Portland cement mortar specimens. This difference indicates that the ranges presented in ASTM C876 and their relationship with rebar corrosion risks are not applicable for alkali-activated materials and it is necessary to provide other criteria for these materials. Also, due to different conductivity of alkali-activated and Portland cement mortars, applying potential difference to accelerate the penetration of chloride ions and comparing the performance of alkali-activated materials with Portland cement is not a correct method. However, this method is suitable for comparing mixes design of alkali-activated mortars and the its results are in accordance with non-accelerated methods.

In this study the sedimentation of nano silica (NS) on graphene oxide (GO) sheets using tetra Ortho silicate (TEOS) hydrolysis in water/alcohol solution and its performance in cement mortar has been investigated. First, the possible interaction between nanoparticles using UV-Vis spectroscopy and electron microscopy (TEM) spectrum is examined. Then, the mechanical properties of the composite material consisting of nano silica and graphene oxide (NS&GO) production was investigated by the Molecular Dynamics Simulation method. The application of nanoparticles on mechanical properties of mortars with and without natural pozzolans has been studied in both individual and composite forms. The dispersion of NS particles on GO sheets can be seen using TEM images through chemical pretreatment and without using surfactants. The results obtained from Molecular Dynamics Simulation indicate a 75% increase in the amount of tolerable stress and a 250% increase in the Young’s modulus of the composite material relative to single NS particles. The 28 days compressive and tensile strength of mortars containing composite nano materials also increased by 31% and 100%, respectively, compared to the control design. Proper dispersion and distribution of nanoparticles, nano silica nucleation property, graphene oxide stepping properties and high zeolite pozzolanic activity have improved the mechanical properties of mortars.

Salt scaling of concrete pavements is known as a serious problem in cold regions. In the present study the effect of water-binder (W/B) ratio, silica fume and air entraining on the salt scaling resistance, compressive strength and electrical resistance were investigated. Microstructure of the concretes was assessed by mercury intrusion porosimetry and scanning electron microscope. Water-binder ratios were 0.35, 0.40 and 0.45. Silica fume was used, by 8% weight of cement, in the predetermined mixtures. The results showed that the best salt scaling resistance was correspondent to the air entrained silica fume specimens. By reducing the water-binder ratio, the amount of surface scaling was decreased. The MIP results declared that silica fume refined the microstructure and also decreased the total porosity and critical pore radius compared with those for the reference specimens. Furthermore, the MIP results of the silica fume specimens declared that the pores smaller than 10 nano were increased, due to the effective pozzolanic reaction. The scanning electron microscope images showed that the concrete containing silica fume had a denser gel compared with those for the reference ones. Introducing silica fume into the specimens had remarkable effect on the later age electrical resistance of the concrete. It was concluded that the highest electrical resistance belonged to the durable specimens. The results of the present study clarify how the micro structure may influence the salt scaling resistance of concrete pavement, this achievement will surely reduce the cost of rehabilitation of concrete pavements in the cold regions.

Portland cement production is known as an environmental pollutant and high energy consuming industry. One way to reduce cement production and consumption is to use supplementary cementious materials. Pozzolans are widely used as supplementary cementing materials (SCMs) nowadays. Due to the widespread use of Portland cement in the construction industry, partial replacement of PC with SCMs such as calcined clays can reduce the harmful environmental impacts of cement production and enhance the durability of concrete structures and increase service life.In this study, the mechanical properties and durability of OPC and concretes containing Calcined Clays (CCs) and Limestone powder (LS) have been compared.In this research, the effect of using calcined clays (CC) and limestone powder (LS) as SCMs on mechanical properties and durability of concrete was investigated. Six concrete mixtures have been prepared by replacing 30% of PC by 3 different CCs and LS as binary and ternary blended mixtures (LC3 mixtures). Mechanical properties, permeability and durability of concrete mixtures containing different CCs have been investigated by means of compressive strength, water absorption, electrical resistivity and rapid chloride migration test (RCMT). According to the results, although using binary and ternary blended mixtures have reduced the compressive strength compared with control mixture, but the permeability and durability of mixtures have been significantly improved.

Concrete pavements are widely used by pavement engineers due to their advantages over flexible pavements such as longer lifetime, good performance and durability, etc. However, concrete pavements represent some drawbacks such as shrinkage that increases the tensile stress in concrete, which may lead to cracking, warping, etc. Drying shrinkage is the most important type of shrinkage in concrete pavements. polypropylene fibers can be used to control or reduce width of cracking by bridging both sides of crack. In this study, the effect of Emboss fiber on the behavior of concrete pavement was investigated. Slump, compressive strength, third-point flexural strength, electrical resistance, skid resistance, free shrinkage and restrained shrinkage by ring test were performed. Two water-cement ratios of 0.35 & 0.4 were used for mix design and the percentage of polypropylene fiber used in mixtures was respectively 0.44% by concrete volume. The results showed that the use of Emboss Fiber reduced the workability of concrete. Also, these reinforcements had different effects on compressive and flexural strength and electrical resistance depend on homogeneity of Emboss fiber reinforced concrete. Furthermore, toughness indices and energy absorption of concrete were significantly increased by using Emboss fiber reinforced concrete. In addition, using fiber indicated a slight reduction in the amount of free and restrained shrinkage and occurrence of first-crack. polypropylene fibers had a key role in controlling crack width by bridging both sides of crack. Finally, no certain relationship was observed between using SRA and changing the skid resistance of concrete pavement.

Successive deterioration in concrete structures which is caused by the acid attack has increased the need for substantial and costly repairs to deal with the destruction of concrete structures. Common devastation of water transfer tunnels is due to sulfuric acid attack. One of the ways of maintenance of such structures is to perform the protective coating of the cementitious and geopolymer coating mortars, in which the different features of this coating layer should be studied.In this study, the mechanical properties and durability of geopolymer and cementitious coating mortars containing granulated blast furnace slag and natural pozzolan have been compared. Five cementitious mortar mixtures were prepared with water to binder ratio of 0.32, binder content of 450 Kg/m3, and replacement of Portland cement (PC) with 20 and 40% slag and natural pozzolan. 2 geopolymer mortar mixtures with KOH and NaOH as activator were designed. To evaluate their mechanical properties Compressive strength and tensile adhesion strength were carried out. Also, in order to investigate their durability features against sulfuric acid attack, mortar specimens length Change, compressive strength loss, and weight loss were investigated. According to the results, the use of cement substitute materials (furnace slag and natural pozzolan) reduced the compressive strength by 25%, increased the adhesion strength by 50%, and reduced the length change, weight loss and compressive strength loss of the samples exposed to sulfuric acid. Also, the use of geopolymer mortars had the better performance in aggressive acidic environments compared to cement-based mortars.

Concrete pavements are widely used by pavement engineers due to their advantages over flexible pavements such as longer lifetime, good performance and durability, etc. However, concrete pavements represent some drawbacks such as shrinkage that increases the tensile stress in concrete, which may lead to cracking, warping, etc. Drying shrinkage is the most important type of shrinkage in concrete pavements. To prevent or reduce the amount of cracking, shrinkage reducing admixture (SRA) can be used. This admixture controls shrinkage by reducing water surface tensile in capillary tubes. In this study, the effect of shrinkage reducing admixture on the behavior of concrete used in concrete pavement was investigated. Slump, compressive strength, third-point flexural strength, electrical resistance, skid resistance, free shrinkage and restrained shrinkage by ring test were performed. Two water-cement ratios of 0.35 & 0.4 were used for mix design and the percentage of shrinkage reducing admixture used in mixtures was 2% by weight of cement. The results showed that the use of SRA had negligible effect on workability. Also, the use of SRA caused about 10% reduction in compressive and flexural strength and electrical resistance. Furthermore, a reduction of 10% and 20% was observed in free and restrained shrinkages, respectively, followed by a 40% reduction in crack width and more than one week delay in occurrence of first crack. Finally, no certain relationship was observed between using SRA and changing the skid resistance of concrete pavement.

A laboratory study was performed to determine the benefits of micro and macro fibers in roller-compacted concrete (RCC) for concrete pavements by measuring the RCCs mechanical and durability properties. To this aim three polymer fiber reinforced RCC mixtures with use of micro and macro polyolefin-based and polypropylene-based fibers in two volumetric content (1 and 2 kg/m3) were prepared and their mechanical properties including the compressive strength and flexural strengths (measured as modulus of rupture and toughness as energy dissipation and durability properties including salt scaling under freeze and thaw cycles and water permeability were evaluated. The results showed that, the macro fibers (as polyolefin-based fibers) could be efficiently enhanced the toughness in comparison with the micro fibers (polypropylene-based fibers). Moreover, the water permeability under pressure of both micro (polypropylene-based fibers) and macro fibers as (polyolefin-based fibers) reinforced concrete decreased up to 20% in comparison with the reference concrete. Furthermore, it was found that the application of micro fibers in comparison with macro fibers significantly improved the salt-scaling resistance of roller compacter concrete.

Acidic environments lead to rapid destruction in the reinforcement concrete structures. Chloride ions also lead to rebar corrosion. The aim of this study is to represent an appropriate mortar which resists against each of the acidic and chloride attack. For this purpose, three types of cement with combination of pozzolans (micro silica and pumice/trass) were used as 10 mix designs. Experiments consisted of compressive strength, capillary absorption and water permeability as general tests, and tests which control the performance of specimens against acid attack (compressive strength reduction, weight loss) and chloride attack (surface electrical resistivity, rapid chloride migration test). Results showed that until the age of 240 days, combination of 5% micro silica and 8% trass in slag cement would be an appropriate mix design for mortar against both chloride and acid attack. Usage of 10% pumice as a substitution of trass in the mentioned mix design performed well too.

Durability of cement based material due to its uses in the building industry, always has been recognized as one of the main components of sustainable development of infrastructure and urban buildings. One way to improve the durability of concrete, especially in corrosive environments is to use natural pozzolans. On the other hand, with increasing carbon dioxide gas production in cities, the effects of carbonation phenomenon on the durability properties of concrete have increased. In this research, the effect of carbonation phenomenon on the durability properties of mortars containing natural pozzolans is investigated. In sample making two natural pozzolans including Khash pumice and Jajroud trass as substitute for cement by 20% and three water/cement ratios of 0.485, 0.44 and 0.4 were used. In this study, compressive strength test was used as an indicator of mechanical properties as well as an indicator of hydration degree in specimens. In order to study of durability properties of mortars carbonation depth, water absorb capillary and electrical resistance of specimens were measured. According to results, use of natural pozzolans reduces the compressive strength of specimens and increase depth of carbonation in them. Also, electrical resistance increases in samples. The results of capillary absorb water test show that carbonation phenomenon decreases capillary absorption coefficient in some samples. Finally, it can be concluded that the trass samples showed better performance than the pumice at an early age, while the pumice improved with increasing age. It is expected that the pumice performance was better than the pumice with give over time

The deterioration of concrete structures is a non-linear and complex phenomenon which is caused by different phenomena. Carbonation is known as one of the major reasons of concrete deterioration. Carbonation has two different effects on concrete structures. Carbonation may have a positive effect against corrosive materials because of its effect in reducing the concrete porosity by changing calcium hydroxide to calcium carbonate. On the other hand, carbonation may have a major role in improving corrosion by reducing the pH of concrete and omitting of passive layer. Although literatures on carbonation have been vast, there are so few studies in carbonation of concrete containing silica fume. In this research the effect of carbonation in reducing of the porosity of concretes containing silica fume was studied. For this reason, concrete specimens with different water to binder ratios (w/c = 0, 0.35 and 0.5) and silica fume percentage (S.F = 0%, 5% and 10%) were made and carbonated in different ages (28 and 90 days). The porosity of carbonated concretes compared with control specimens by different experiments. Finally, a mathematical model for concrete porosity reduction under carbonation phenomena was developed based on experimental results.

Roller-compacted concrete (RCC) is a special blend of concrete that has essentially the same ingredients as conventional concrete but in different ratios, and without slump. It was shown that the application of fibers would enhance some properties of concrete, however in roller compacted concrete; there was a lack of knowledge. The application of RCC gained a great attention for physical, mechanical, durability and economical benefits. In this paper, the effects of synthetic polymeric fibers on the physical and mechanical of fiber roller compacted concrete pavement were experimentally investigated. To this means, three mixtures by using of micro and macro polymeric fibers made. The mechanical strength tests including compressive and flexural strength and also abrasion strength tests were carried out. The results showed that the application of synthetic polymeric fibers improves the mechanical (including the compressive strength, flexural strength) and physical properties (abrasion strength) of fiber reinforced roller compacted concrete (FRCC).

Geopolymers are alumino-silicate polymer that formed by alkali activation of Si and Al rich materials. This paper describes the effects of different alkaline solution types and concentrations, modulus of sodium silicate and sodium silicate to alkaline solution ratio on the flowability and mechanical properties of alkali activated slag and the optimum activator has been determined for the slag- based geopolymers production.Results reveal that adding the sodium silicate largely enhances the workability and compressive strength of slag-based geopolymer paste.The optimum modulus of sodium silicate and sodium silicate to alkaline solution ratio to reach the maximum strength are 2.33 and 0.4 respectively. At 91 days of curing, the compressive strength of the optimum mixture of slag- based gepolymer is about 74 % more than the compressive strength of ordinary Portland cement paste.

Due to the high amount of CO2 emission through the production of cement and great energy consumption in the cement industry, one of the most important issues in concrete technology is to find out an appropriate replacement for Portland cement. Alkali activated materials are the new approach for solving this problem. In fact, alkali activated concrete consists of an inorganic structure containing two parts: Source material and alkaline activator liquid. In this study, the effect of the amount of source material and water to binder ratio on chloride ions ingress was evaluated. For this purpose, 5 mix designs were used to make alkali activated slag concretes and for activating slag, 6 molar potassium hydroxide and sodium silicate solutions were employed as alkaline activator liquid. Additionally, one mix design was dedicated to ordinary Portland cement concrete for the sake of comparison.
The properties of AAS concretes were examined by means of slump loss, measurement of compressive strength at the ages of 1 to 180 days and capillary water absorption test at 7, 28 and 90 days. Furthermore, chloride ions penetration was measured through electrical resistivity test, rapid chloride migration test (RCMT) and resistance against chloride ions diffusion test according to NT Build 443. The results indicated that the performance of water to binder ratio and also the amounts of source material were comparable to that of ordinary Portland cement concretes. Additionally, alkali activated slag concretes had higher compressive strength and also superior durability against chloride ions penetration compared to OPC concretes

In this paper in order to the evaluation of Fiber Reinforced Polymer (FRP) sheets’ durability in less time, marine simulator was designed and built similar to the tidal zone of Persian gulf. In addition of tidal modeling, cyclic radiation of UV, high emperature and humidity were other parameters that were controlled in this environment. The changes in the mechanical properties of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) sheets, bonding strength of sheets to concrete and the effect of wrapping were investigated by putting the specimens in the marine environment. Ultimate strength and elastic modulus of CFRP sheets decreased by 2% and 18%, respectively. These values were 28.8% and 17% for GFRP sheets, respectively. Bonding strength reduction of FRP sheets to concrete was 13.9% and 15.9%, respectively for CFRP and GFRP sheets. Also ultimate strength of confned specimens was decreased by 11.6%, 41% and 34%, respectively by wrapping with one layer of CFRP, one and two layers of GFRP after exposure. The reduction value of modulus of plastic region was 17%, 18% and 12% for these specimens respectively.

Concrete, as a main construction material has an alkali nature which makes it vulnerable to attack by acidic solutions. Therefore, investigations on performance of various types of concretes against different kinds of acid attacks are essential to achieve durable concretes in severe environments. Considering the significant effect of durability in sustainability of concrete structures, high performance concrete (HPC) which is characterized by its high compressive strength, low permeability and fine durability in many severe environments, is increasingly utilized in civil and infrastructural constructions. This paper presents an experimental study on durability of HPC and conventional concrete (CC) containing ordinary Portland cement (PC), ground granulated blast furnace slag (GGBFS) and natural pozzolan (NP) under sulfuric acid attack. Compressive strength, ultra-sonic pulse velocity determination, capillary water absorption test and evaluation of electrical resistivity were utilized to investigate mechanical properties and permeability of hardened concrete. The durability properties were studied through measurement of weight and compressive strength loss, ultra-sonic pulse velocity variations and length change of mortar prisms exposed to sulfuric acid. The results indicated that concretes containing less cementitious materials and mineral admixtures were more durable in acidic solutions, and incorporating higher volume of GGBFS and NP could improve performance of concrete against sulfuric acid attack.

Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete’s resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.

Groundwater and seawater usually contain both chloride and sulfate ions. These two salts destroy concrete reinforcement by rebar corrosion and making expansion respectively. In order to investigate the influence of sulphate ions on chloride penetration in mortar, visual method, penetration profile and rapid chloride migration test results are compared with each other. According to the results until the age of 208 days, Sulfate ions lead to decrease the chloride penetration in control samples and a little increase in silica fume samples. Regarding to Trass Samples, an intermediate state is occurred; low sulfate content solution decreases and high sulphate content solution increases chloride penetration into these samples. According to different results of RCMT and common penetration tests in combined solutions, behavior of control samples is not predictable by RCMT method. However, visual investigation and profile penetration method demonstrate a similar trend in aspect of comparison. This research shows that the absolute penetration depth is catched by visual method does not have enough accuracy.