3/29/2023 0 Comments White pages california khatib![]() In spite of the excellent qualities developed by MK as pozzolanic material, the possible conversion of some hexagonal hydrates (C 2ASH 8 and C 4AH 13) at elevated temperatures could result in problems in its use. ![]() Subsequently, Frías and Cabrera, reported that MK has a positive effect on the pore size distribution of pastes with 10%, 15%, 20% and 25% of MK cured at 20 ☌ for up to 360 days and demonstrated a good statistical relationship between the degree of hydration and the porosity. Khatib and Wild reported a refinement of the pore structure and a total intruded pore volume increase between 14 an 28 days for pastes with 5%, 10% and 15% of MK. MK has been shown to modify the pore size distribution of mortars and pastes cured at 20 ☌. The proportion, appearance, evolution and stability of these phases depend on different factors including the chemical and mineralogical composition of MK, the MK/lime ratio, the presence or absence of activators and the temperature, ,, ,,. The pozzolanic reaction between MK and lime at 20 ☌ produces the cementitious compounds C 2ASH 8 and C 4AH 13 and CSH gel. This phenomenon could lead to negative influences on durability aspects, particularly in large volume mass concrete causing thermal stress, cracking and loss of strength. and subsequently Bai and Wild reported that, due to its high pozzolanic activity, the temperature rise in MK-blended pastes can be greater than that observed in plain OPC at early ages, due to the double exothermic effect of the pozzolanic and hydration reactions. Recently, some activated materials such as metakaolin (MK), which is obtained by thermal activation of kaolinite, have been shown to be excellent pozzolans. By-products as pozzolanic additions are also routinely used for the manufacture of commercial portland cements and high-performance concretes, due to their positive influence on the microstructure and durability of blended concretes,. Natural pozzolans have been used since antiquity with excellent results for the production of durable concrete. A suitable correlation between porosity and degree of hydration has been found. Therefore, the hydrated phases produced in MK-blended cements under the test conditions used do not have a negative effect on the microporosity. The results show that there is no increase in porosity values and average pore diameters with time. An estimated degree of hydration of MK-blended cements cured at 60 ☌ is proposed. time is determined using mercury intrusion porosimetry (MIP). The total, partial porosity and average pore diameter evolution vs. ![]() The partial or total conversion reaction could produce a negative effect on the performance and durability of blended cements, due to a volume decrease associated with the process of transformation.ĭue to the influence that this conversion could have on the microstructure and durability of a cement paste containing MK, the current paper presents the results of a research programme carried out on blended cements containing 10%, 20% and 25% of MK, cured at 60 ☌ up to 124 days of hydration. However, some of them (C 2ASH 8 and C 4AH 13 ) are metastable phases, converting to hydrogarnet (C 3ASH 6 ) for long curing times at elevated temperatures. It has been reported that CSH, C 2ASH 8 and C 4AH 13 are the most important hydrated phases formed. ![]() When MK reacts with calcium hydroxide, cementitious products are formed. ![]()
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