Feasibility of predicting compressive strength for alkali-activated slag concrete by Maturity method

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Feasibility of predicting compressive strength for alkali-activated slag concrete by Maturity method

ارائه دهنده: Provider: Zahra safari

اساتید راهنما: Supervisors: Mahmoud nili (Ph.D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Mohammad shooshtari (Ph.D) Mostafa moghadasi (Ph.D)

زمان و تاریخ ارائه: Time and date of presentation: march 13, 2021 at 12:00

مکان ارائه: Place of presentation:

چکیده: Abstract: Concerns about greenhouse gas emissions during cement production have led to efforts to develop more environmentally friendly cementitious materials. Therefore, cement is partially replaced by supplementary cementitious materials, SCM, such as Ground granulated blast furnace slag. The mineralogy and chemical composition of slag varies from source to source and also does not provide a unique temperature threshold for proper setting performance of concrete containing cement substituted by slag. it is necessary to study the setting performance of Isfahan Ground granulated blast furnace slag; Because the construction schedule of concrete structures is significantly affected by the timing and development of compressive strength. On the other hand, in order to completely remove cement, the use of alkaline activators in concrete containing slag is considered. One of the disadvantages of SCM on concrete performance, especially at low curing temperatures, is the increase in setting time and the reduction of initial strength, which can be a problem in the field in terms of planning construction operations. Serviceability problems observed in concrete structures, including human and financial losses due to inaccurate estimates of compressive strength development considers the need to determine the temperature sensitivity in the section on predicting the maturity of concrete. Since the initial hydration reaction is different from older ages; it is recommended not to use the unique activation energy in the equivalent age equation. To address this situation, an experimental study has been planned to develop and validate a procedure for estimating the compressive strength of environmentally friendly concrete by the maturity method. The present research study considers two aspects of ecology and prediction of concrete properties. The first aspect introduces and evaluate the setting, thermal regime, compressive strength, water absorption and microstructure of concrete containing slag without and with activator and the second case Takes into account the ASTM C1074 validation objectives for concrete containing slag without and with activator, determination of activation energy during setting and hardening period, prediction of setting and compressive strength properties and finally presents the proposed relationship of compressive strength prediction. For this purpose, in the cast of concrete mixtures, 4 replacement of 0, 50, 75 and 100% slag with water to cement ratio of 0.5 and 2 replacement of 0 and 100% slag with water to cement ratio of 0.4 is considered and In casting alkali activated mixtures, water to cement ratio of 0.4, three concentrations of 11.25, 15 and 18.75 M of sodium hydroxide and liquid sodium silicate with silica modulus of about 2.3 has been used. In casting the equivalent mortar mixtures, two ratios of water to cementitious materials was 0.5 and 0.4 to evaluate the development of compressive strength according to ASTM C 1074 and the setting time of paste mixtures with normal concentration. All mixtures were measured under three curing temperatures of 8, 23 and 40 ° C. The results obtained from the present study show that in all paste and concrete mixtures, temperature has an accelerating effect on setting time; however, in mixtures containing a percentage of slag, a longer setting time has been observed. It was not possible to measure the setting time of concrete containing 100% slag; but concrete containing 50% slag is introduced as a suitable alternative to ordinary concrete at high temperatures. The peak of the temperature history curve is delayed by increasing the slag replacement percentage. The development of compressive strength of concrete containing slag is also different from ordinary concrete due to the reduction of compressive strength at early ages. On the other hand, slag has reduced the negative effect of temperature increase on the later ages compressive strength and the cross over effect of the compressive strength curve has not occurred. Also, Adding slag improves durability in the long ages. However, the lowest compressive strength corresponding to the highest measured water absorption occurred in the 75% replacement slag mixture. The effect of increasing the amount of slag on the outer silicate gel product causes a gradual morphological change from a completely linear fibrillar at low slag replacement to a fine foil-like structure at high slag values. Activation energy at early ages, obtained from the setting time results, is directly related to the increase in the percentage of slag replacement. But in hardening period, this relationship is indirect. On the other hand, the activation energy of equivalent mortar with an error of about 10% represents the activation energy of the corresponding concrete. Except in the mixture containing 75% slag, which is especially evident in the fit with the hyperbolic function. Prediction of setting time cured under 8 and 40 ° C based on the equivalent age relationship is associated with an error of more than 20%, and if a maximum of 50% error is accepted, this proposal can be used to predict the setting time of concrete using the equivalent age method. The equivalent age relationship has more accurately estimated the effect of temperature on the development of compressive strength at an early age for all mixtures than the Saul approach. In addition, compressive strength of concrete is underestimated by using the activation energy of equivalent mortar. In general, the prediction of compressive strength in case of using the activation energy of initial setting time of concrete and temperature sensitivity of the setting process and hardening period of concrete in the equivalent age method, can be provided with appropriate accuracy. Also, the development of compressive strength of concrete containing 50% slag has been predicted better with hyperbolic function, but the mixture of 75% slag and alkali-activated slag has been determined well with exponential function. The validation results of the proposed relationship with previous studies compared to ASTM C 1074 in the later ages are well approximated. Abstract: Concerns about greenhouse gas emissions during cement production have led to efforts to develop more environmentally friendly cementitious materials. Therefore, cement is partially replaced by supplementary cementitious materials, SCM, such as Ground granulated blast furnace slag. The mineralogy and chemical composition of slag varies from source to source and also does not provide a unique temperature threshold for proper setting performance of concrete containing cement substituted by slag. it is necessary to study the setting performance of Isfahan Ground granulated blast furnace slag; Because the construction schedule of concrete structures is significantly affected by the timing and development of compressive strength. On the other hand, in order to completely remove cement, the use of alkaline activators in concrete containing slag is considered. One of the disadvantages of SCM on concrete performance, especially at low curing temperatures, is the increase in setting time and the reduction of initial strength, which can be a problem in the field in terms of planning construction operations. Serviceability problems observed in concrete structures, including human and financial losses due to inaccurate estimates of compressive strength development considers the need to determine the temperature sensitivity in the section on predicting the maturity of concrete. Since the initial hydration reaction is different from older ages; it is recommended not to use the unique activation energy in the equivalent age equation. To address this situation, an experimental study has been planned to develop and validate a procedure for estimating the compressive strength of environmentally friendly concrete by the maturity method. The present research study considers two aspects of ecology and prediction of concrete properties. The first aspect introduces and evaluate the setting, thermal regime, compressive strength, water absorption and microstructure of concrete containing slag without and with activator and the second case Takes into account the ASTM C1074 validation objectives for concrete containing slag without and with activator, determination of activation energy during setting and hardening period, prediction of setting and compressive strength properties and finally presents the proposed relationship of compressive strength prediction. For this purpose, in the cast of concrete mixtures, 4 replacement of 0, 50, 75 and 100% slag with water to cement ratio of 0.5 and 2 replacement of 0 and 100% slag with water to cement ratio of 0.4 is considered and In casting alkali activated mixtures, water to cement ratio of 0.4, three concentrations of 11.25, 15 and 18.75 M of sodium hydroxide and liquid sodium silicate with silica modulus of about 2.3 has been used. In casting the equivalent mortar mixtures, two ratios of water to cementitious materials was 0.5 and 0.4 to evaluate the development of compressive strength according to ASTM C 1074 and the setting time of paste mixtures with normal concentration. All mixtures were measured under three curing temperatures of 8, 23 and 40 ° C. The results obtained from the present study show that in all paste and concrete mixtures, temperature has an accelerating effect on setting time; however, in mixtures containing a percentage of slag, a longer setting time has been observed. It was not possible to measure the setting time of concrete containing 100% slag; but concrete containing 50% slag is introduced as a suitable alternative to ordinary concrete at high temperatures. The peak of the temperature history curve is delayed by increasing the slag replacement percentage. The development of compressive strength of concrete containing slag is also different from ordinary concrete due to the reduction of compressive strength at early ages. On the other hand, slag has reduced the negative effect of temperature increase on the later ages compressive strength and the cross over effect of the compressive strength curve has not occurred. Also, Adding slag improves durability in the long ages. However, the lowest compressive strength corresponding to the highest measured water absorption occurred in the 75% replacement slag mixture. The effect of increasing the amount of slag on the outer silicate gel product causes a gradual morphological change from a completely linear fibrillar at low slag replacement to a fine foil-like structure at high slag values. Activation energy at early ages, obtained from the setting time results, is directly related to the increase in the percentage of slag replacement. But in hardening period, this relationship is indirect. On the other hand, the activation energy of equivalent mortar with an error of about 10% represents the activation energy of the corresponding concrete. Except in the mixture containing 75% slag, which is especially evident in the fit with the hyperbolic function. Prediction of setting time cured under 8 and 40 ° C based on the equivalent age relationship is associated with an error of more than 20%, and if a maximum of 50% error is accepted, this proposal can be used to predict the setting time of concrete using the equivalent age method. The equivalent age relationship has more accurately estimated the effect of temperature on the development of compressive strength at an early age for all mixtures than the Saul approach. In addition, compressive strength of concrete is underestimated by using the activation energy of equivalent mortar. In general, the prediction of compressive strength in case of using the activation energy of initial setting time of concrete and temperature sensitivity of the setting process and hardening period of concrete in the equivalent age method, can be provided with appropriate accuracy. Also, the development of compressive strength of concrete containing 50% slag has been predicted better with hyperbolic function, but the mixture of 75% slag and alkali-activated slag has been determined well with exponential function. The validation results of the proposed relationship with previous studies compared to ASTM C 1074 in the later ages are well approximated.

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