Evaluation and Testing of Carbonation Behavior of Sprayed Concrete with Different Liquid Accelerators
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Abstract This article mainly tested and evaluated the carbonation resistance of sprayed concrete mixed with different liquid accelerators, and thus attempted to establish a prediction model for the carbonation depth of sprayed concrete. Firstly, the influence of alkaline liquid accelerator based on sodium aluminate (AR), alkaline-free liquid accelerator based on aluminum sulfate (AS), and alkali-free liquid accelerator based on fluoroaluminate (AF) on carbonation resistance of sprayed concrete was explored. In addition, the porosity and pore structure distribution of ordinary sprayed concrete (OSC), sprayed concrete with AR (SC-AR), sprayed concrete with AS (SC-AS), and sprayed concrete with AF (SC-AF) were analyzed by the mercury intrusion porosimetry. The carbonation depth and compressive and splitting tensile strength also were tested. Furthermore, the scanning electron microscopy was employed to observe the micromorphology of hydration products. The experimental results indicated that the carbonation depth order of sprayed concrete was as follows: SC-AR > SC-AF > SC-AS > OSC. After analyzing the disparity of SC-AR, SC-AS, and SC-AF carbonation depth caused by AR, AS, and AF dosage, the influence coefficients of sprayed concrete carbonation depth were introduced. Finally, the carbonation depth prediction models of SC-AR, SC-AS, and SC-AF were preliminarily established.Keywords:
Porosimetry
Carbonatation
Pervious concrete
The carbonation resistance of high volume mineralad mixtures concrete(HCMAC) was studied with the purpose of investigating the main reason that leaded to the serious carbonation of readymixed concrete.There sults of artificial accelerated carbonation test showed that the 28 days carbonation depth of HCMAC,with 380kg/m3 total usage of cementitious materials,is morethan 3 times of that of concrete without any mineralad mixture.So,high volume of slag power,flyash(Ⅱgrade)and high-calcium fly ash would lead to the decrease of the carbonation of concrete by a bigmargin.
Carbonatation
Cementitious
Slag (welding)
High calcium
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Carbonation is mainly known as a deterioration phenomenon for reinforced concrete structures. However, it has also a beneficial effect when we consider transport of aggressive species. This study aims at developing an optimized technique, in terms of quantification of carbon dioxide uptake, to control the carbonation of cement-based materials and to examine the permeability of the carbonated specimens. Samples were embedded in a special cell and subjected to an elevated CO2 pressure at the upstream side. The CO2 uptake was measured in the up-and downstream part by precise mass flow controllers. The experiments were performed on hardened cement. Post-analysis techniques like TGA, XRD and pH measurents were used to determine the phase changes, hence the carbonation front, while MIP and nitrogen adsorption were used to characterize the microstructure changes The effect of carbonation on the general transport behaviour was studied by measuring changes in the water permeability. Results show that the carbonation of fully saturated sample was very slow. Even this limited carbonation leaded to a decrease in permeability by one order of magnitude.
Carbonatation
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Carbonation is the results of the interaction of carbon dioxide gas in the atmosphere with the alkaline hydroxides in the concrete. In other words, of the hydrates in the cement pastes, the one which reacts with CO₂in air readily is Ca(OH)₂, the product of the reaction being CaCo₃, and which decreases the alkalinity of concrete. Consequently, RC structures is deteriorated due to steel corrosion in concrete. An overview of the mechanism of carbonation and carbonation induced corrosion are presented in this paper. Moreover, many factors influencing carbonationof concrete, the investigation results for coronation of domestic RC structures, the techniques of controlling carbonation with respect to materials and measured for deteriorated RC structures due to carbonation induced steel corrosion are discussed.
Alkalinity
Carbonatation
Carbon steel
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The aim of the study is to investigate compressive strength of pervious concrete by reduction of fine aggregate from zero to 100%, additionally investigate infiltration rate of pervious concrete. Experimental study has conducted at Cecos Engineering University Peshawar. The pervious concrete samples were produced for 7 and 28 days. Compressive strength of pervious concrete indicated higher reduction of the sand reduces compressive strength and almost 50% compressive strength decreased by reduction of 100% sand from the design mix. On the other side, infiltration rate for 28 days shows direct relation above 40% reduction of sand and highest 273% of infiltration rate by reducing 100% sand from the design mix. The 90% reduction of sand from concrete give considerable compressive strength of 2150 psi and infiltration rate of 165.79 inch/hour, which can be recommended for pavements of parking and walking area.
Pervious concrete
Infiltration (HVAC)
Strength reduction
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Carbonatation
Vaterite
Slag (welding)
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Understanding the changes in the pore solution upon carbonation is crucial with respect to comprehending the mechanisms of reinforcement corrosion in carbonated mortar or concrete. In this paper we used Cold Water Extraction (CWE), a rapid leaching method, on profile ground powder from partially carbonated Portland cement and Portland-fly ash cement mortars to study changes in the pore solution composition. Carbonation decreased the free alkali metal content measured with CWE, which matched with the portlandite profiles determined by thermogravimetry and the carbonation depth detected with pH indicator. The alkali metal uptake by carbonation products was confirmed by SEM-EDS and thermodynamic modelling. Besides the decrease in the alkali metal concentration in the pore solution upon carbonation, we observed for both binders a considerable increase in chlorine and sulphur concentrations. This can further accelerate corrosion in carbonated concrete.
Portlandite
Carbonatation
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Carbonatation
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