Abstract
This paper proposes a technique to prevent the corrosion of steel reinforcement in concrete based on slag cement (SC) activated by Na(K) salts of strong acids (SSA) in the composition of by-pass cement kiln dust (BP). The technique implies using additional modifiers in the form of the Portland cement CEM I 42,5 R and the calcium-aluminate admixture (CAA) С3А∙6H2O.It is shown that adding the Portland cement contributes to enhancing the intensifying influence of BP on the SC hydration, accompanied by an increase in the strength of artificial stone. This effect is predetermined by the formation of hydrosilicates in hydration products with an increased crystallization degree in the form of CSH(I) and C2SH(A).Modifying SC with CAA ensures the intensive formation of low-soluble AFm phases in the composition of hydration products, aimed at reliable binding the SSA anions (Cl-, SO42-) that are aggressive to steel reinforcement.The study result has established the possibility to produce SC, activated by SSA, when using BP, the Portland cement, and CAA. Mathematical methods to plan the experiment were applied to produce an SC composition of "granulated blast furnace slag – BP – Portland cement – CAA", characterized by a strength class of 42.5 and a molar ratio of Cl-/OH- in a porous solution not exceeding 0.6. The resulting properties predetermine the feasibility of using SC in steel-reinforced concrete.The relevance of this work is due to the modern trends in the development of the construction industry. The introduction of cement that contains mineral additives, in particular granulated blast furnace slag, contributes to improving the environment by reducing СО2 emission. The use of such cement as a base of steel-reinforced concrete ensures the increase in their functionality and durability
Highlights
Current trends in the development of the construction industry predetermine the relevance of introducing the so-called “green” materials whose production involves resource- and energy-saving technologies [1] implying a responsible attitude towards the environment [2]
For the accelerated formation of AFm phases, represented by the system of complex salts 3CaO∙Al2O3∙CaSO4∙nH2O, 3CaO∙Al2O3∙CaCl2∙10H2O, 3CaO∙Al2O3∙Ca(OH)2∙nH2O, we propose the introduction of CAA in the form of hexahydrous tricalcium calcium aluminate (С3А∙6H2O)
We have proven the activating influence of SSA in the BP composition on the hydraulic properties of GBFS, due to the influence of strong alkali NaOH formed from an exchange reaction involving calcium at a content of BP about 30.0 %
Summary
Current trends in the development of the construction industry predetermine the relevance of introducing the so-called “green” materials whose production involves resource- and energy-saving technologies [1] implying a responsible attitude towards the environment [2]. The use of BP, which is a large-ton byproduct of the cement industry, as a source of SSA to improve the hydration activity of GBFS is a promising way of developing the construction industry, predetermined by a series of factors such as increasing the content of alkalic metal oxides in the Portland types of cement; transition to a dry production technique of the Portland cement clinker; using fillers containing active silica. Despite the validity of using SSA, including as part of BP, to activate the SC, there is an issue related to insufficient strength of the latter This task is resolved by the additional involvement of activators in the form of “classical” compounds of alkaline metals. The use of SSA, which, for example, are included in BP composition, to activate SC is related to the need to ensure sufficient strength of such cement Another problematic issue is to counter the aggressive effects of the anionic residue of strong acids on steel reinforcement in concrete
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