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Journal Jul 2019

Impact of sulphate on chloride-induced corrosion of steel in concrete U. Raghu Babu, B. Kondraivendhan

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.

Strength behaviour of reinforced recycled aggregate concrete columns confined with ferrocement laminate Lekshmi S. Thilakan, Saji. K. P.

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.

Impact of salinity in netravati estuary sand on durability of reinforced cement concrete Raveesha P., K. E. Prakash, B. T. Suresh Babu

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.

Development of graded geopolymer concrete Annapurna, Ravande Kishore

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.

Influence of shear span to depth ratio on structural parameters of geopolymer - psc beams S. Kumar, S. Rajendra

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.

Generation of P-M interaction design charts for rc shear walls Bijily Balakrishnan, Indu Geevar, Jithin K. V., Devdas Menon

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.

Point of View : Self-curing (Internally cured) concrete using porous light weight aggregates : A better solution for the sustainable development Dada S. Patil, Shrishail B. Anadinni

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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