Chloride Ion Diffusion Resistance of Bulk Hydrophobic Concrete: Comparison of w/c and Dosages

Post-cast application of hydrophobic agents onto hardened concrete is successful at reducing external ion diffusion into cement paste, this work examines pre-cast application of hydrophobic admixtures in fresh concrete. Concretes, with water to cement ratios (w/c) 0.45 and 0.50 (CEM I; low C(3)A), were mixed. Adding alkyltrialkoxysilane or triacylglycerol admixtures ranging from 1 to 3 wt%(cem) in these concretes were evaluated. Increasing the dosage of hydrophobic admixtures decreased the compressive strength. The usage of these admixtures did not hinder the further development of the microstructure as all concretes gained strength after one year, but not in the same percentage increase as the reference concrete.Chloride ion diffusion, after exposure to 3 wt% NaCl solution at 20 degrees C for 91 days, in concretes with 1 wt%(cem) admixture showed slight reductions in diffusion rate (8-17%) compared to the reference. At 3 wt%(cem), triacylglycerol admixtures showed better hindering effects of inward chloride diffusion, this was especially evident in w/c = 0.45. Equivalent addition of alkyltrialkoxysilane-based admixtures increased the diffusion of chloride ions transferred into the cement matrix

Durability and service life prediction of reinforced concrete structures

This paper presents some durability and service life models for reinforced concrete structures with regard to chloride ingress, carbonation and frost attack. In the past years a number of models for durability design of concrete structures have been suggested by relevant organisations or international committees. It is necessary to validate these models against long-term field data for their applicability with respect to exposure climate in order to satisfactorily use the models in the durability design and redesign of concrete structures. In this study, various potential models for concrete resistance to chloride ingress, carbonation and frost attack were briefly reviewed. Three models including the simple ERFC, the DuraCrete and the ClinConc, for prediction of chloride ingress were evaluated using the infield data collected from both the field exposure site after over 20 years exposure and the real road bridges of about 30 years old. A physicochemical model for prediction of carbonation depth was evaluated using the infield data collected from the field exposure site after 11 years exposure and the limited data from the real structures with the age of 7-13 years. For the modelling of frost attack, some problems in measurement of critical saturation degree and actual degree of saturation are discussed. According to the comparison results, the simple ERFC overestimates whilst the DuraCrete model underestimate the chloride ingress in most cases. The ClinConc model on the other hand gives reasonable good prediction for both the short-term (one year) and the long-term (21 years) exposure. The Papadakis model for carbonation also gives fairly good prediction of carbonation depth when compared with the Norwegian infield data classified as exposure class XC3, but underestimates the carbonation depths when compared with the infield data from Norwegian structures in exposure class XC4. For the frost attack, it is premature to apply the models to the service life prediction so far

Experimental study of the material and bond properties of frost-damaged concrete

In an extensive experimental investigation, several types of tests were conducted on a reference specimen and frost-damaged concrete. Two levels of internal frost damage were quantified by the relative dynamic modulus of elasticity and compressive strength. Test results showed a significant influence of freeze-thaw cycles on the compressive strength and even more influence on the modulus of elasticity and the compressive strain at peak stress. Reduced tensile strength and increased fracture energy were measured. From inverse analysis of wedge splitting test results, a significant effect of frost on the shape of the tensile stress-crack opening relationship was observed: tensile strength was reduced, while the post-peak behaviour was more ductile for the frost-damaged concrete. Pull-out tests showed the influence of freeze-thaw cycles on bond strength and slip. The pull-out test results are compared with similar tests available in the literature and the effect of frost on bond behaviour is discussed

Influence of frost on the bond between steel and concrete

One of the severe types of deterioration in concrete structures is associated with the volume expansion of concrete caused by freezing and thawing of concrete. Frost damage in concrete is caused by the volume expansion of freezing water in the concrete pore system. Thereby, tensile stresses are initiated and micro and macro-cracks are introduced into the concrete body, which leads to a type of severe damage known as internal frost damage. This mechanism not only affects the material properties of concrete such as tensile and compressive strength and elastic modulus of concrete, but also, influences the bond strength between the reinforcement and surrounding concrete in damaged regions

Influence of frost on the bond between steel and concrete

One of the severe types of deterioration in concrete structures is associated with the volume expansion of concrete caused by freezing and thawing of concrete. Frost damage in concrete is caused by the volume expansion of freezing water in the concrete pore system. Thereby, tensile stresses are initiated and micro and macro-cracks are introduced into the concrete body, which leads to a type of severe damage known as internal frost damage. This mechanism not only affects the material properties of concrete such as tensile and compressive strength and elastic modulus of concrete, but also, influences the bond strength between the reinforcement and surrounding concrete in damaged regions

Ringprovning av betongs frostbeständighet enligt SS 13 72 44. - Fördjupad undersökning år 2001

Swedish Standard SS 13 72 44, better known as the "slab test", is used in Sweden and the Nordic countries, as well as in some other parts of Europe, to test the scaling resistance of concrete. In Sweden a large number of laboratories have tested concrete according to the "slab test" for over 10 years. To ensure the repeatability and the reproducibility of the test method the accredited laboratories regularly carry out round-robin tests under supervision of the Swedish Board for Accreditation and Conformity Assessment (SWEDAC)

The influence of ageing on the salt-frost resistance of concrete

Abstract This thesis presents the results of an investigation of the influence of ageing on the salt-frost resistance of concrete. The ageing mechanisms investigated were hydration, drying and carbonation. Specimens of ‘micro’-concrete, either with OPC alone as the binder or with silica or slag as part of the binder, were freeze/thaw tested at different ages after casting. Prior to testing, the specimens were conditioned for 7 days in climate chambers specially built for the purpose, creating climates with increased CO2 (~1 vol-%) and with no CO2 at all, both at 65 % RH and +20 °C. Water-cured, never dried, specimens were tested as well. The results show that ageing has a strong influence on the salt-frost resistance, and that carbonation is the most dominant ageing mechanism. The effect differs, however, for concretes with different binder types/-combinations. For concrete made with OPC alone, or with silica (up to 10 %) or slag (up to about 30 %), carbonation leads to a significantly improved salt-frost resistance. For concrete with high slag contents (over about 50 %) carbonation leads to a markedly poorer salt-frost resistance. The properties of the pore structure of carbonated and uncarbonated mortars were further investigated by capillary suction and by measuring the freezable water content. Results show that carbonation leads to substantial changes of the pore structure and therefore of the freezable water content. It is proposed that, although different for different materials, it is this substantial change in pore structural properties that is the primary cause of the observed influence of carbonation on the salt-frost resistance. A limited XRD investigation of carbonated materials with and without slag as part of the binder showed no marked difference in carbonate phases formed. For both materials calcite was the dominant phase. As a complement to the laboratory investigations, field investigations were carried out at three exposure sites; two situated in saline environments (marine and highway), and one in a salt-free environment. A comparison shows that results from the laboratory investigations correspond well with the experience from up to seven years exposure at the exposure sites

Verification of a rapid technique for corrosion measurement using reinforced concrete slabs after long-term field exposure

This paper presents the results from the measurement of reinforcement corrosion in slabsafter over 13 years’ exposure in the marine environment, using a newly developed rapid nondestructivetechnique. In the beginning of 1990’s over 40 reinforced concrete slabs withdifferent types of binder and water-binder ratios were exposed in a real marine environment atSwedish west coast. In the past years a rapid technique for non-destructive measurement ofcorrosion was developed at SP Technical Research Institute of Sweden. The technique isbased on the classic galvanostatic pulse technique with the time-dependent behaviour ofpolarisation taken into account and the mathematical modelling for estimation of currentdistribution. The technique was implemented into a handheld instrument for easy use in thefield. This instrument was used to measure the corrosion conditions of the steel barsembedded in the concrete slabs exposed in the field site. Based on the results from the nondestructive measurement, the actual corrosion of steel bars in five concrete slabs was visually examined. The results from the visual examination show that the newly developed rapid technique is a useful tool with reasonably good accuracy for assessment of corrosion of steel in concrete. It has been found that the corrosion rate measurement is the most reliable parameter, while the half-cell potential and resistivity can only be used as complementary parameters in the assessment of corrosion status

Microstructural changes caused by carbonation of cement mortar

The change of specific surface area and pore size distribution due to carbonation of an ordinary Portland cement mortar is investigated. The adsorption of water vapor on noncarbonated and well-carbonated cement mortar is measured in order to evaluate the difference in specific surface area for the two samples using the BET theory. From the measured desorption the pore size distribution is calculated using the Kelvin formula. A sorption balance is used to measure the sorption characteristics for the two studied sample qualities. In this method dry and saturated air are mixed in desired proportion in a closed system. One of the benefits of the method is that the samples not are exposed to carbon dioxide during testing, i.e., undesired effects caused by carbonation on the sorption can be eliminated. The specific surface area for a noncarbonated sample was calculated, using the measured adsorption data, to be 8% higher than for the well-carbonated sample. The difference in pore size distributions was more marked than the difference in specific surface area for the two samples. The well-carbonated mortar had about twice as much volume attributed to small pores as the noncarbonated cement mortar