Reaction products, structure and properties of alkali-activated metakaolin cements incorporated with supplementary materials – a review

Process Design for a Production of Sustainable Materials from Post-Production Clay

“…AAC can be generated from a wide range of aluminosilicate precursors, with differing availability and value worldwide. Calcined clays, and especially metakaolin, have become a significant part of the raw materials base of AAC, and can be used both, as a main aluminosilicate precursor of AAC and as a supplementary component in blended activated systems [ 2 ]. The most precursor materials used in AAC are structurally disordered, being either glassy (e.g., FA, blast furnace slag) or thermally disrupted layer structures (e.g., metakaolin and other calcined clays) [ 3 , 4 , 5 , 6 ].…”

“…Therefore, this class of materials is very versatile and locally adaptable [ 7 , 8 , 9 ]. According to most researchers, the key to their reactivity is average particle size, thus the specific surface area (usually in the range 1.20–38 μm and 2.16–22 m 2 g −1 , respectively), and the strain in the bonding network is induced by thermal dihydroxylation [ 2 ]. Depending on the raw material components used, AAC can be divided into three main categories: Cement with high calcium and silicon content [((Na, K) 2 O–CaO–Al 2 O 3 –SiO 2 –H 2 O system); the raw materials such as blast furnace slag or clay (SiO 2 + CaO > 70%) are alkali-activated, however, the high-pH condition is not required; the first product of the reactions is dominated by a calcium silicate hydrate (C–S–H) and a small percentage of calcium aluminosilicate hydrate (C–A–S–H) gel with a tobermorite-like (mostly Q 2 , and some Q 1 and Q 3 ) structure; Cement with low calcium, but higher aluminum and silicon content ((Na,K) 2 O–Al 2 O 3 –SiO 2 –H 2 O system), the raw materials such as metakaolin, granulated blast furnace slags, class F fly ash, are activated by sodium hydroxide (NaOH) or potassium hydroxide (KOH) at a higher pH than that required for the materials with high calcium content, the reactions tend to generate a sodium aluminosilicate hydrate phase (N–A–S–H) with a highly crosslinked (mainly Q 4 ) disordered pseudo-zeolitic structure; Hybrid cement formed as the result of the alkaline activation of materials with CaO, SiO 2 and Al 2 O 3 contents >20% ((Na,K) 2 O–CaO–Al 2 O 3 –SiO 2 –H 2 O]–[(Na,K) 2 O–Al 2 O 3 –SiO 2 –H 2 O), they include materials with a low Portland cement clinker content and over 70% of mineral additions (slag, FA) or blends containing no Portland cement (blast furnace slag, phosphorous slag, and FA); the reaction products are very complex and include C–A–S–H (containing sodium) and (N,C)–A–S–H (high calcium content N–A–S–H) gels [ 10 , 11 , 12 ].…”

“…The reaction, structure, and property of the resulting products are also controlled by several other factors, including the type the alkaline activator, alkali activation time and conditions, curing conditions etc. [ 2 , 13 ].…”

Alkali-Activated Metakaolin and Fly Ash as Unfired Ceramic Bonding Systems

“…It can be used especially in the construction industry as a filler in plasters, stucco and concrete mixtures, fireproof coatings, it is used in the production of paints or refractory materials. Several works dealing with the metakaolin AA process can be found, for example, Rakhimova et al published the comprehensive review about the products of metakaolin alkali activation and their properties [17], similarly Rashad [18] provided the review regarding to alkali-activated metakaolin covering the hydration, the effect of the curing conditions and other important topics. Great emphasis is placed on the temperature regime of kaolinite to metakaolin transformation as evident for example from the paper published by Gasparini et al [19].…”

Modification of the structure of gypsum-cement-pozzolanic binder

“…At the same time, the new time requires the development of new structural and composite materials in conjunction with new technologies. Complex environmental and economic conditions in Russia also determine a new approach to the creation, production and use of building materials for various functional purposes [1][2][3][4][5]. At the same time, special attention should be paid to resource conservation, maximum use of local raw materials and waste from various industries, increasing the competitiveness of construction products, and using efficient high-tech technologies and materials.…”