The aim of the present investigation is to evaluate the effect of admixed chloride, sulphate and chloride-sulphate solutions on the corrosion performance of rebar in concrete, as well as the influence of metakaolin (MK) and red mud (RM) blended concrete. The performance of the rebar was monitored by corrosion current density values using linear polarization resistance technique. The changes in electrical resistivity due to the presence of salts and different binder type reflects the corrosion behavior of rebar. Hence, the present study extended to monitor the variation of electrical resistivity in concrete. In order to achieve the guidelines of ASTM G16-13, the statistical analysis was carried out on the data of corrosion current density. The results indicated that the presence of magnesium sulphate increases the corrosion rate in both OPC and MK blended concrete. However, the analyzed results indicated that the passivity zone increases with conjoint presence of sulphate and chloride ions as internal source, and the risk of the corrosion shifted from moderate to severe and severe state to very high. It implies that once the corrosion initiated, the corrosion rate of rebar is high in concrete admixed with composite solution of chloride-sulphate ions than that of admixed with pure chlorides. The concrete blended with MK performed better as compared to OPC concrete in terms of higher electrical resistivity and lower chloride induced corrosion current density with and without presence of sulphate ions.
In this study, attempts have been made for the use of recycled aggregate in place of normal coarse aggregate in reinforced concrete columns. It includes processing of recycled aggregates and then obtaining their physical and mechanical properties. Both compressive and flexural strength of concrete mixes decrease with increase in the percentage of recycled aggregate added. To analyse compression behaviour of ferrocement confined, reinforced recycled aggregate concrete columns, six column specimens were cast. Out of which, one column from each of the two size-groups is kept as control column, one each is strengthened using ferrocement and the remaining for assessing the effect of retrofitting with ferrocement. It is observed that ultimate strength of confined specimens increased significantly. A comparison with results of two analytical models showed higher ultimate strengths than obtained in the experiments.
The influence of ingredients in concrete plays an important role in the serviceability and durability. The region where sea and river meets is termed as Estuary. The water available in estuary is saline due to intrusion of sea water. The density of sea water is more than the fresh water and settles down, forms a layer around the sand particles. This sand has high influence on durability of reinforced cement concrete. Netravati estuary was selected for the present study to know the effect on concrete. Ten samples were collected along the estuary in one kilometer interval from the mouth of sea. The locations were identified as N1, N2, N3, N4, N5, N6, N7, N8, N9 and N10. The specimens were fabricated as per IS 456. The Half-potential test results show increase in length of estuary from mouth, there is decrease in corrosion rate. This study concludes that sand from estuary used in concrete highly influence on corrosion rate.
Fly ash based Geopolymer concrete (Fly ash based GPC) is emerging as a potential replacement to normal concrete due to its environmental friendly nature. Supplementing to this GPC is becoming a promising material because of non usage of Portland cement and usage of waste material like Fly ash, Ground Granulated Blast furnace Slag (GGBS) etc. Grade designation of concrete is very important to use in various structural applications. However no code is available to do the mix design of GPC based on grade of concrete, i.e. allotment of mix designations based on strength. Previous literature reveals that several parameters such as alkaline liquid ratio, aggregate proportion, percentage GGBS addition, molarity of NaOH and type of curing influence compressive strength of GPC. Hence in the present study parametric optimization method is chosen to identify parameters influence on compressive strength of GPC and based on optimum compressive strength, proportions for different grades of GPC are identified. Further Scanned Electron Microscopic (SEM) and Energy Dispersive X Ray (EDX) study is carried out on proposed grades of GPC.
An experimental investigation is undertaken to study the basic structural parameters of post-tensioned Geopolymer concrete beams, subjected to flexural and shear failure by varying the shear span to depth ratio ( α / D ) under two point loading. Shear span to depth ratio is considered as the main criteria which influences on structural behaviour of beams. Effects of shear span to depth ratio on some of the structural parameters like load factor, deflection, ductility, shear capacity and mode of failure of PSC beams made of geopolymer concrete mixes are evaluated and discussed.
Reinforced concrete (RC) shear walls resist lateral loads in a building due to wind and earthquake, in addition to gravity loads. Each rectangular shear wall segment (sometimes provided with ‘boundary elements’ at the ends) is required to be designed to resist axial compression (P) combined with inplane bending moment (M). This paper provides closed-form expressions for generating the full P-M interaction curve for the design and analysis of shear walls with and without boundary elements, which has been validated with SAP. It also gives normalised load/moment expressions for generating design charts, similar to SP 16 charts for RC columns. The simplified method given in IS 13920 is applicable only for rectangular shear walls with uniformly distributed main reinforcements. The proposed method provides a more accurate and economical solution than the simplified method given in IS 13920.
Proper curing of concrete structures is very important to meet performance & durability requirements. Curing allows continuous cement hydration & subsequently continuous gain in the strength. Lack of proper moisture conditions virtually slows down the hydration of the cement. Hydration practically stops when the RH within the pores falls below 80%. The conventional curing is achieved by externally applied water after hardening of concrete. Concrete must be properly cured if its optimum properties are to be developed. This reduces porosity to a level such that the desired strength & durability can be attained & volume changes in the concrete due to shrinkage are minimized. Concrete which dries out quickly undergoes considerable early age drying shrinkage. This is a primary reason for weak, powdery surfaces with low abrasion resistance. Lack of proper curing increases permeability & absorptivity. This affects the durability of concrete. Permeability & absorptivity are the functions of porosity of the concrete. Durability depends on whether these pores & capillaries are discrete or interconnected.
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