Hydration heat modeling of high replacement slag concrete | |
| Author | Pa Pa Win |
| Call Number | AIT Thesis no. ST-99-9 |
| Subject(s) | Hydration Slag cement Hydration Slag cement |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. |
| Publisher | Asian Institute of Technology |
| Abstract | Microcracks happen in massive concrete structures due to the internal temperature rise as a result of exothermic chemical reaction of cement. Since concrete possesses low thermal conductivity, the condition inside it is close to the adiabatic one. Among the various techniques of solving this temperature rise problem; the utilization of pozzolans like blast furnace slag as cement replacement material is one of the powerful tool for many reasons. Slag is hydraulic blending material and because of this, it shows two opposite manners on hydration process of cement when used as cement replacement material. It has physical effect of acceleration on hydration heat rate by serving additional nucleation site for precipitation of hydrates from cement which we called "filler effect". Since slag itself can react with Ca (OH)2 as well as water, it cannot serve totally as filler effect. The filler effect largely depends upon its reaction condition. But as opposite extreme cases, like high replacement cases, the slag reaction will stagnate due to the shortage of activator or water, its behavior rather similar to the inert powder and filler effect will be prominent. For filler effect, the ratio of total surface area of slag and cement is used as a base factor and also affected by shortage of Ca(OH)2 and water. It will accelerate after stage II of C3S. While hydrating, eventhough chemical reaction of slag depend on availability of activator, it can show its active and hydraulic behavior before degree of hydration of about 10%. Within this stage, regardless of the amount of activator in the solution if it is in activator ambient and its water soluble parts react freely with water. Ca(OH)2 present in the solution act as catalyst for their reaction. So there is no chemical reduction effect of slag on hydration of cement. After that, the shortage of Ca(OH)2 and free water in the solution plays an important role and retard the hydration heat rate of blended material up to some extent. At and after the Degree of hydration of slag 10%, negative values of available Ca(OH)2 found in the analysis are set to be zero because slag can behave as inert powder in the absent of activator, but the excess amount of Ca(OH)2 (positive values ) are kept for next step of calculation. Overall behavior of blended cements with pozzolans is reduction of hydration heat rate, although consideration are taken as one accelerating (due to physical effect) and the other reduction effect (due to chemical reaction). Implementation of above considerations for slag material into multi-component hydration heat model (COMH3) has been successfully executed the matching results of experimental and analytical values on verifications make the model more complete and a useful tool. |
| Year | 1999 |
| Type | Thesis |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Construction Engineering and Infrastructure Management (CM) |
| Chairperson(s) | Toshiharu Kishi;Toshiharu Kishi; |
| Examination Committee(s) | Pennung Warnitchai;Nii, Kazuyoshi;Somnuk Tangtermsirikul; |
| Scholarship Donor(s) | Government of Japan; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1999 |