Assessment of the Effectiveness of Different Curing Practices in Addis Ababa

Aregawi, Samson Walelign (2014) Assessment of the Effectiveness of Different Curing Practices in Addis Ababa. Masters thesis, Addis Ababa University.

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Abstract

Curing is defined as a process of maintaining adequate moisture and favorable temperature in concrete for the hydration reaction to continue. The main advantage of curing is to keep the internal humidity of concrete to the desired level. Different researches showed that if the internal humidity of concrete is below 80% the rate of hydration will be reduced and if it goes below 30% the reaction will even cease. Therefore curing is the most significant process in order to keep the internal relative humidity to the required amount because it is through hydration reaction concrete develops the desired properties, which are mechanical properties and durability. This research work has two objectives. The first one is assessing the current curing practices and to study the awareness given to curing. And the second objective is assessing the effectiveness of current curing practices in Addis Ababa. To meet the above mentioned objectives questionnaire was used for the first objective and experimental study was also conducted for the second objective. For the experimental study, tests were conducted in two phases. In both phases tests were conducted in rich mortar mixture with cement to sand ratio of 1 to 2.5. In the first phase water absorption and compressive strength tests were conducted to correlate compressive strength and absorption test results. The objective of the first phase was to check the acceptability of compressive strength test for measuring the effectiveness of current curing practices. And the objective of the second phase was to assess the effectiveness of current curing practices by conducting compressive strength test on mortar samples, which were subjected to different curing practices. In ACI 308R-01, there are methods for assessing the effectiveness of curing. These are tests by monitoring the quantitative changes on the immediate environment, by monitoring the environmental conditions, by monitoring the moisture and temperature of concrete and by measuring the physical properties, etc… From the above mentioned tests we can understand that monitoring curing effectiveness is all about checking whether there is adequate moisture so that the hydration reaction will continue. In assessing the effectiveness of current curing practices the 70% criteria from ACI 308R-01, which says “at time of termination of curing the concrete has to develop 70% of the specified strength”, was used. It is the researcher opinion that two terms „adequacy‟ and „effectiveness‟ of curing has to be seen separately. Adequacy of curing is all about efficiency of curing for the development of the desired properties. Assessing the adequacy of curing for the development of the desired properties of concrete by conducting tests on mortar specimens may not be good enough unless there is a developed correlation between compressive strength and absorption capacity of mortar and concrete specimens. Because the adequacy of curing is a function of exposure condition, mixture proportion and properties under question. But there are researches which correlate properties of mortar and concrete. One finding showed that there is a clear relationship between compressive strength of mortar and concrete. A given curing method can be adequate for the desired compressive strength but it may not be adequate if durability is desired. But when we say curing effectiveness it is the ability of the curing method in creating suitable condition for the paste phase to have “complete‟ hydration so that the pore size and pore distribution will be minimum. In this research the compressive strength of standard laboratory cured samples are assumed to be the full potential of the mixture. Therefore, if the field curing doesn‟t allow the development of at least 70% compressive strength of the standard laboratory cured samples at time of termination or 85% at 28th day, the curing is considered to be ineffective. Effectiveness of curing is related with ability of curing to create a suitable condition in order to have “complete” hydration of the paste phase. Results from questionnaire survey showed that water sprinkling twice a day for 7 days with and without burlap is mostly practiced curing method. Another finding from the questionnaire survey showed that most of the practitioners are aware of the benefits of curing and consequences of lack of it. But when we see on the implementation it was found poor. From the experimental study; current curing practices were found to be very poor in creating suitable condition for the hydration of cement so that the desired properties can develop. Based on the 70% criteria the current curing practices were found ineffective for mixtures with a w/c less than 0.5. Although water-cement ratio of 0.5 is greater than required for “complete” hydration, but sealed curing is found ineffective. One major reason is late application of curing.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Curing, Curing Affected Zone, Curing Effectiveness, Mortar, Compressive Strength, Water Absorption
Subjects:	Q Science > Q Science (General) T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TD Environmental technology. Sanitary engineering
Divisions:	Africana
Depositing User:	Andriamparany Edilbert RANOARIVONY
Date Deposited:	20 Nov 2018 09:16
Last Modified:	20 Nov 2018 09:16
URI:	http://thesisbank.jhia.ac.ke/id/eprint/7581

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