Amir Mohammad Ramezanianpour

An Accelerated Test Method of Simultaneous Carbonation and Chloride Ion Ingress: Durability of Silica Fume Concrete in Severe Environments

The effects of simultaneous carbonation and chloride ion attack on mechanical characteristics and durability of concrete containing silica fume have been investigated through an accelerated test method. Specimens containing different amounts of silica fume were maintained in an apparatus in which carbon dioxide pressure and concentration and relative humidity were kept constant, and wetting and drying cycles in saline water were applied. Surface resistivity, sorptivity, CO2 consumption, and carbonation and chloride ion ingress depths measurements were taken. Phase change due to carbonation and chloride ion attack was monitored by XRD analysis, and microstructures and interfacial transition zones were studied by implementing SEM as well as mercury intrusion porosimetry. It was expected to have a synergistic effect in the tidal zone where simultaneous carbonation and chloride ion attack happen. However, the observed reduced surface resistivity, compared to specimens maintained in CO2 gas, could be due to the moisture that is available near the surface, hindering CO2 from penetrating into the pores of the specimens. Moreover, the porosity analysis of the specimens showed that the sample containing silica fume cured in the tidal zone had 50.1% less total porosity than the plain cement paste cured in the same condition.

Effect of Supplementary Cementing Materials on Concrete Resistance Against Sulfuric Acid Attack

Concrete durability is an inevitable consideration for sustainability of structures in aggressive environments. Therefore, the recent investigations are mainly based on the improvement of concrete durability such as resistance of concrete against acidic solutions attacks. This paper presents the experimental study on durability of concretes containing ordinary Portland cement (OPC), blast furnace slag (BFS) and natural pozzolan (NP) immersed in sulfuric acid solution. Mechanical properties and permeability of hardened concrete were determined by compressive strength and capillary water absorption tests. In addition, the durability properties and degradation intensity were studied through the measurement of weight loss, compressive strength loss and changes in ultra-sonic pulse velocity (USPV) in concrete specimens.

Pervious concrete reactive barrier containing nano-silica for nitrate removal from contaminated water

In this research, the effectiveness of using pervious concrete as a reactive barrier to decrease the concentration of nitrates in polluted water was investigated. Parameters of concrete mix design including water to cement ratio (W/C), aggregate to cement ratio (A/C), the amount of nano-silica (NS), and fine aggregates (FA) were studied based on Taguchi method. Properties of concrete such as compressive strength, density, permeability, and porosity, as well as pH measurement and the column method were carried out to assess the nitrate removal capacity of pervious concrete. Also, SEM-EDX, XRD, and FTIR were used to analyze the results. It was found that the optimum mix design in terms of nitrate removal corresponded to the mix with W/C = 0.26, A/C = 5, NS = 6%, and FA = 20%. Based on the results, it can be said that adding NS (up to 6%) and FA (up to 20%) to pervious concrete had the best influence on nitrate removal and compressive strength. Addition of NS increased the nitrate removal capacity due to increase in surface positive charges and provision of new surface functional groups.

Mechanical Properties and Chloride Ion Penetration of Alkali Activated Slag Concrete

Compared to ordinary Portland cement (OPC) concrete, alkali activated compounds refer to inorganic materials that cement is not the main constituent in their mixes. In fact, alkali activated concretes have two main parts in their binder structure: source material and alkaline activator liquid. In this study, the binder consists of blast furnace slag as a source material and sodium silicate solution (wt. ratio: SiO2/Na2O = 2.33) and 6 M potassium hydroxide which are incorporated as alkaline activator liquids. Since there are several parameters that affect the properties of these concretes, 9 alkali activated concrete mix designs are utilized to investigate the influence of source material amount, solid part of alkaline activator, solid part of sodium silicate solution and the ratio of water to binder. Furthermore, one mix design for OPC concrete is performed to compare with alkali activated slag (AAS) concrete characteristics.

Investigation on the Effect of Shrinkage Reducing Admixtures on Shrinkage and Durability of High-Performance Concrete

Because of the advances in material science, new materials are launched to market that make it possible to produce concretes with more desirable properties for technical applications. These new concretes that cannot be made using the common materials and mixing ratios are called high-performance concretes. High-performance concretes are usually made with a low water-to-cement (w/c) ratio and high cement contents. High-performance concrete and its properties have gained the attention of engineers in recent years. One of the major shortcomings of cement-based materials such as concrete is their shrinkage. In this study, the effect of shrinkage-reducing admixture (SRA) on the shrinkage and durability of concrete is investigated. To examine SRA effects on shrinkage, free and constrained shrinkage tests are carried out while taking into account the impact of changing w/c ratio and cement content. Moreover, to study the durability of high-performance concrete, tests are carried out on durability parameters, including electrical resistance, depth of water penetration under pressure, and the percentage of water absorbed by the concrete. The results show that the use of shrinkage-reducing material decreases free shrinkage of concrete. When applying a lower w/c ratio and higher contents of cementitious materials, the use of this substance has a greater impact. Constrained shrinkage test results also indicate that the use of SRA additive causes a significant increase in the time of shrinkage crack formation during the test. The results of the durability tests indicate significantly improved durability properties of concrete aged 28 days.