The 72 concrete cubes were oven-dried at 105±5 °C until constant weight, not more than 0.1 % weight change over 24 hr drying period is achieve. Moisture content is define, as the ratio of difference between (wet weight-dry weights) to wet weight and it is express as percentage. Then conditioned concrete cubes were fully submerged in water until it attains moisture content (Mc = 5%) as per the requirement of the present research work. This attainment of moisture content (Mc
= 5%) in the present research work is designate as fully saturated conditioned concrete cubes. The ISAT was carry out on 72 pre-fully saturated conditioned concrete cubes with six designed mixtures type (M1-M6). The pre-fully saturated conditioning of concrete cubes was archived by fully submerged specimens in the water until its reached fully saturated condition (Mc = 5%). As observed from results that, ISAT was increase in all mixtures type (M1-M6) at 10 min. Actually ISAT was increase at early stage (10 min) as compared to 30 min and 60 min, which was, varied about 16.89% as well as 33.10% respectively. Similarly, the ISAT was observe to increase at early time duration (10 min) as compared to longer time duration at 30 min and 60 min in which it is varied as 20.14% as well as 37.05% for in mixtures type (M1-M3). Whereas in case of mixtures type (M4-M6), the ISAT was slightly increased at early stage (10 min) as when compared to longer time duration at 30 min and 60 min which was varied about 13.64% as well as 29.15% respectively.
Furthermore the ISAT values was more decreased as when compared to DCC and PSC concrete cubes in all mixtures type (M1-M6).
3.6.5 Summary
In the present research work, the designed mixtures type was characterized in 72 concrete cubes of size (100x100x100 mm) by ISAT in dry/wet condition (Mc = 0%, Mc =2.5%, and Mc =5%) with water in order to evaluate near surface characteristics of concrete. In turn to study an effectiveness of compressive strength on ISAT in different mixtures type. In which, the first mixtures type (M1-M3) was designed as higher compressive strength (40 N/mm2) with varied slump value (0-10, 10-30, and 60-180 ) mm, and in second mixtures
Chapter 3 Experimental programme type (M4-M6), its comprised of different compressive strength (25, 30, 40 N/mm2) with constant slump value (10-30) mm.
An extensive information about water permeability of the near surface layer of concrete could be obtain through ISAT. Moisture content can have negative influence on measured results of various types of concrete. The moisture content was reduced water absorption capacity and thus it is advisable to dry test specimens prior to testing in the ISAT. ISAT value in DCC concrete cubes was to be more as when compared to PSC and FSC concrete cubes.
Similarly, ISAT value was more in PSC as when compared to FSC concrete cubes. ISAT value was more at an initial time duration for higher compressive strength and goes on decreases with an increased time duration. Similarly, ISAT value was more at initial time duration for lower compressive strength, goes on reduces with increased time duration and compressive strength in all pre-conditioned concrete cubes.
It is determined from the results that, ISAT value with moisture content (Mc =5%) was found to be predominantly decreased as when compared to DCC and PSC (Mc =2.5%) concrete cubes in all designed mixtures type.
Salt ponding test on concrete cubes 3.7.1 Introduction
In worldwide the use of de-icing salts has been common since 1960 in areas where snow and ice is a seasonal roadway safety hazard, automobile, and highway bridge corrosion, and ecosystem changes caused by deicing salt is well documented and focus of considerable study until now in recent years. The salts are necessary to provide safe winter driving conditions and save lives by preventing the freezing of a layer of ice on roads and bridge decks. However, the safety and sense of comfort provided by the salts is not without a price, as these salts can greatly contribute to the degradation and decay of reinforced concrete transportation systems. Most salts are chloride-based and when the applied salts diffuse into the concrete and reach the level of the steel reinforcement, the chloride ions can quickly de-passivate the steel and activate corrosion reactions that can ultimately result in the loss of functionality of the concrete structure. Furthermore, research has indicated that these same salts attack the concrete itself, through reactions and phase changes,
Chapter 3 Experimental programme producing dimensional changes and cracking of the concrete. The further penetration of the salts into these cracks sets up a vicious cycle of concrete spalling and degradation.
Actually, the total amount of moisture contained within the concrete, as either water or water vapour, is call as the moisture content. Moisture in concrete is present in the capillary pores and smaller gel pores within the concrete matrix. Moisture may exist as either water (when the concrete is wet and the pores are saturated) or as water vapour, which provides a level of relative humidity within the concrete material. The initial source of moisture in concrete is the mixing water that is use at the time of manufacture. Water is add to the concrete during batching to allow hydration of the cement and provide the workability required to place and finish the concrete. Some water will be lost through bleeding and evaporation and some amount will be consume by the hydration process. Either a small quantity of water will remain following hydration of the cement in the minute spaces (capillary pores) within the concrete, or within the hydration product, themselves (gel pores). Almost all forms of deterioration in reinforced concrete involve ingress of deleterious fluids through the pore structure of the concrete. In particular, the ingress of chlorides is a major cause of early deterioration of reinforced concrete structures due to subsequent corrosion. In saturated concretes, fluids will enter through diffusion whereas partially saturated concretes, fluids will be absorb by capillary suction. In reality most concrete are in a continual flux between saturated and partially saturated states, as they undergo continuous cycles of wetting and drying.
The corrosion of reinforcement bars due to chloride ingress is a well-known problem in reinforced concrete. Several methods have been adopt to protect reinforced concrete, and one of them is to provide added protection to the concrete surface in the form of surface treatments. They react with the cement matrix and form a hydrophobic layer on the walls of the pores within the concrete. This protects the concrete from the ingress of water and water-born salts. However, too much water in the pores of concrete will prevent the treatments from penetrating deeper into the pores. Actually, the depth of penetration and therefore the durability of the treatment is adversely affect when the concrete is near saturation. In fact, billions of dollars could be spend annually to replace defective infrastructure that needs replacement only because of concrete failing to attain its expected service life. The cost is due to the effects of chloride ingress into the concrete removing protective sheaths from steel reinforcement leading to destructive corrosion of the infrastructure. Thus accurate prediction of the rate of chloride ingress into concrete would lead to the establishment of proper specification in turn achieve designed service life. There are currently many types of protective materials for reinforced concrete structures and the influence of these materials in the chloride diffusion coefficient still needs more research.
Chapter 3 Experimental programme The primary focus of this present study is to examine an effects of wetting and drying with 10%
sodium chloride solution in concrete cubes with/without impregnation material (solvent based and water based) for about 160 days. In fact that, the chloride concentration stability was maintain over entire salt ponding, test period by covering the concrete specimens with plastic cover in order to avoid evaporation of chloride concentration. Chloride profiles of samples exposed to wetting and drying cycles were determined. From these profiles, the rate and depths of chloride ingress were calculated and compared for six different mixtures type of concrete. There have been a number of studies in which, the chloride penetration profile of concrete exposed to a chloride solution for different defined periods. But in this present research work, chloride concentration at different drill depths such as 30-40-50 mm was interpreted in order to evaluate chloride diffusion coefficient by using Fick’s second law for in case of concrete cubes with/without impregnation material for six different mixtures type.