Papers by Keyword: Chloride Penetration

Abstract: Metakaolin is considered as one of most promising pozzolanic microfiller material in concrete industry. Metakaolin is a high value product obtained from kaolin clay calcined at high temperatures which also can be effectively used in ceramic industry therefore its application in concrete industry is rather limited. In present research metakaolin containing waste (MKW) by-product was studied as a partial cement replacement in high strength self compacting concrete (SCC). Obtained waste material derives from the foam glass granule production plant where kaolin clay is used as releasing agent during heating process and in the end metakaolin with glass impurities is obtained as by-product. In present research 5 to 15 wt.% of cement was replaced by MKW. A constant water amount was used for all mixtures and workability (>600 mm by cone flow) was ensured by changing the amount of superplasticizer. Compressive strength was tested at the age of 7, 28 and 180 days. To determine durability of SCC the chloride penetration was tested according to NT BUILD 492, freeze-thaw test according to LVS 156-1:2009 annex C and alkali-silica reactivity test according to RILEM TC 106-AAR-2. The results indicate that cement replacement by MKW did not affect the strength of SCC significantly. At the age of 28 days SCC with 15 wt.% of MKW reached compressive strength of 70 MPa comparing to 68 MPa to reference mixture. The chloride penetration test results indicated that the non-steady-state migration coefficient of reference samples was reduced 3.7 times and it was concluded that SCC resistance to chloride penetration can be increased by incorporation of MKW in mixture composition. Freeze-thaw test results indicated that obtained SCC can withstand at least 500 freeze-thaw cycles without surface damage and weight loss. It was concluded that up to 15 wt.% of cement can be replaced by metakaolin containing waste without strength loss and the durability of SCC could be increased.

Abstract: The effect of different layers of silane impregnation on chloride resistance of concrete materials at various curing ages is systematically discussed. The chloride resistance of two types of concrete specimens with surface silane impregnation has been investigated through the Rapid Chloride Migration (RCM) method. The testing results indicate that the chloride penetration can be effectively restrained by silane impregnation, and the chloride diffusion coefficients of samples are significantly decreased. After curing for 28 days, when compared to the untreated samples, the chloride diffusion coefficients of two types of concrete specimens both with two layers of silane impregnation decreased by 37.4%, 37.6% respectively.

Abstract: In this paper, two types of modified hydrotalcites (MHT) were incorporated into cement mortars with two dosage levels (replacing 5% and 10% cement by mass). Designated testing programme including strength test, porosity test, and rapid chloride migration and diffusion test were employed to investigate the effect of modified hydrotalcites on chloride penetration in cement mortar. The results based on these tests showed the incorporation of MHT-pAB at 5% dosage in mortar specimens produced a notably improved chloride diffusion resistance with no or minor influence on the development of mechanical strength.

Abstract: This paper presents a review of the studies on chloride penetration of recycled aggregate concrete in terms of its main factors. These factors include quality and replacement ratio of recycled concrete aggregate, mineral admixtures, water-binder ratio, type and level of load and curing mechanisms. Further, some key issues for future research are put up.

Abstract: The eruption of Sidoarjo mud volcano that has been taken place since 2006 had caused significant damage to the local social environment, and until now there is no immediate solution that can be offered. Utilization of the Sidoarjo mud as construction material recently has gained some advancement by calcination of the mud, that make the previously inert material to become more reactive and to be more viable for its use as cement replacement or geopolymer precursor. This paper reports an on-going study to utilize the Sidoarjo mud as precursor of geopolymer by investigating the influence of particle size on the reactivity of the calcined Sidoarjo mud. Furthermore, durability properties of Sidoarjo mud-based geopolymer was also studied. The results show that making finer the mud particles by milling in longer period, using a rod-mill drum for 8 hours, can increase the reactivity of the mud. Compressive strength of geopolymer mortar can increase up to 155% when compared to the ones based on milling time of only 2 hours. Durability properties of sulphate acid resistance and chloride penetration are comparable to fly ash-based geopolymer, while the shrinkage measurement showing higher value.

Abstract: Chloride-induced steel corrosion is worldwide one of the major causes of deterioration of reinforced concrete structures, producing loss of structural strength and stability. One of the most aggressive exposure conditions for concrete is marine environment together with the drying and wetting conditions by tidal and splash action. In such an aggressive environment the presence of cracks has a great influence on chloride ingress.In this paper both the experimental and the numerical results of the influence of artificial cracks on chloride penetration in mortar specimens are presented. The experimental results were obtained using chloride penetration tests on mortar specimens of different sizes, with and without artificial cracks, subjected to a cyclic treatment. Numerical results were obtained using transient finite element analysis by simulating chloride mass diffusionwith COSMOS/FFE realized with the heat transfer modulus T, which was replaced by the total concentration C, and the thermal conductivity K_x, replaced by diffusion coefficient D. Comparisons between the results on chloride penetration concluded that the numerical ones obtained using the mass transfer modulus agree fairly well with the experimental ones. In addition the influence of crack length on chloride ingress was presented.

Abstract: Traditionally main driving force of chloride penetration in concrete have been regarded as a diffusion, however, large construction such as tunnel elements and foundations for bridges can be placed on large sea water depths where the water pressure is fairly different from the pressure in the splash zone. Moreover, hydrostatic pressure increases in proportional to measured depth from the surface of water because of the increasing weight of water exerting downward force from above. In this study, new experiment method to estimate chloride penetration of concrete under water pressure is introduced. The water pressure has a great influence on the chloride penetration and thereby on the service life of marine concrete.

Abstract: As part of the studies on the durability of concrete with machine-made sand, this paper introduces the test results and the forecast model of time-dependent chloride penetration of this kind of concrete. Three strength grades of concrete C30, C40 and C50, and the contents of stone powder in machine-made sand of 5%, 9% and 13% in mass were considered in the mix proportion of concrete with machine-made sand. The ordinary concrete with natural river sand in the same strength grade was tested at the same time for comparison. The test was conducted for 360 days, the results showed that the effect of the content of stone powder on the chloride penetration of concrete was obvious at early curing time of 7 days, and tended to be lower with the increase of curing time. When the curing time was longer than 90 days, this effect could be neglected, and the resistance to chloride penetration of concrete with machine-made sand was almost equal to or larger than that of ordinary concrete. The decrement of chloride diffusion coefficient varied from sharp to gentle with the curing time, the resistance of concrete to chloride penetration increased with the increase of concrete strength. Meanwhile, to facilitate the calculation in practice, the forecast model of chloride diffusion coefficient of concrete is proposed.

Abstract: This paper studied the influence on corrosion resistant performance through the rust resistance performance tests and the resistance to chloride ion penetration tests. In the tests, four test specimens were prepared: (a) blank sample without corrosion inhibitors or composite admixture; (b) mix 20% composite admixture replacing the cement; (c) mix 2% organic inhibitor replacing the cement; (d) combine 20% composite admixture and 2% organic inhibitor replacing the cement. The results showed that both of the composite admixture and the organic inhibitors had the ability to prevent steel corrosion in concrete structures and had their own advantages respectively. Mixing mineral admixture and inhibitor together had synergy effect and had more obvious anticorrosion effect, which helped the specialized production of antirust compound-admixture to ensure homogeneity of concrete.

Abstract: This study aims to determine whether the surface durability of high volume fly ash (HVFA) concrete can be improved by applying alkali solution on its hardened surface. Concentrations of alkali solution and methods of application were studied on several w/cm ratios and replacement percentage of fly ash in concrete mixture proportion to investigate the durability performance. Durability tests conducted were accelerated sulfuric acid attack and ion chloride penetration to investigate the improved durability of HVFA concrete. From the results, it was shown that applying alkali solution on the surface of HVFA concrete can increase its durability performance. The different w/cm ratio and the percentage of fly ash used affect the increase in durability performance. The optimum alkali solution concentration and method of application need further research to determine their effectivity.