Slag-alkali lightweight concrete with corn waste aggregate

. The paper presents a technical solution for obtaining effective slag-alkali lightweight concrete on the basis of corn waste. The granulometric compositions, types and forms of waste at grinding for obtaining slag-alkali lightweight concrete on the basis of corn waste are developed; compositions and formulations of slag-alkali lightweight concrete based on shredded corn waste have been developed. As a result of the development of a new scheme of changing the mechanism of strength formation of slag-alkali lightweight concrete and optimization of its composition, lightweight concrete composites with compressive strength of 2.9-4.5 MPa and bond strength of aggregate with mineral matrix of 45.7-59.7 MPa were obtained.


Introduction
Lightweight vegetable waste concrete is the most common type of concrete in regions with hot and dry continental climates.It has high thermal insulation properties, is environmentally friendly, lightweight and can contain agricultural waste, which is abundant in the steppe regions of Russia and Kazakhstan [1][2][3][4][5].
It has been found that rational construction materials can be produced from corn waste, so technological developments are needed for its production and utilization [6].The paper presents a technical solution for obtaining effective slag-alkali lightweight concrete based on corn waste.

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Materials and methods 1 Corresponding author: as.falconi@yandex.ru,* In experimental studies, shredded corn cobs of LLP "Taraz agro-industrial complex" of the southern region of Kazakhstan were used as cellulose organic filler from agricultural waste.The sizes of shredded corn cobs are presented in Figure 1.Moisture characteristics of corn waste at the time of experimental work were 3-5%.

Fig.1. Size of shredded corn cobs
Slag-alkali composite binders were prepared and tested in compliance with TU 67-1020 "Slag-alkali binders.Technical conditions".According to GOST 310.3 "Method of determination of standard density, setting time and uniformity of volume change", physical and technical properties of cement paste, such as standard density and setting time of cement paste, were evaluated [7,8,9].
In accordance with GOST 10180-2012 "Methods of determination of strength by control specimens", the manufacture and testing of slag-alkali specimens was carried out.
Grinding of slag-alkali binders by fineness of grinding was evaluated at specific time intervals of grinding in the planetary mill "Activator-4M" and mill SVM-3 [10].
The consistency of the slag-alkali mortar was measured on a shaking table by the standard cone method according to GOST 10180-2012 "Methods of determining the compressive and bending strength".

Results and discussions
To select the composition of lightweight concrete, the composition of different morphological parts of corn waste was analyzed.In terms of morphology, corn waste consists of husk, hull, wood and heartwood or core.Corn waste contains 65-67%, husk and bark 27-29%, beans 2-3% and heartwood -about 3% [11].The chemical composition of different forms of corn waste fractions is determined by the content of components in them.
The results of the analysis are presented in Table 1.The studies have shown that corn waste contains substances that are easily hydrolyzed and easily extracted, or "cement poisons".This is detrimental to cement-containing binder compositions and slows down the strength gain of the materials and samples under investigation.For this reason, this deleterious effect on the physical and mechanical properties of the tested lightweight concrete composites is to be neutralized.Studies by previous scientists have shown that soluble monosaccharides such as sucrose, glucose and fructose and some hemicelluloses, which are hydrolyzed to sugars under certain conditions, are the most harmful, while soluble polysaccharides, tannins and resins have the least impact.The alkaline environment of cement-containing mortars contributes to the release of "cement poisons".The amount varies greatly depending on the type, condition and storage of corn waste.
The research also confirmed that the strength of lightweight concrete composites can be increased from 12% to 17% by removing hydrolyzable substances from organic aggregates made from corn waste.Therefore, the presence of substances in the composition of organic aggregate, negatively affecting the quality of concrete, can be considered one of its disadvantages.As corn waste contains relatively large amounts of extractable substances, the authors of this paper modified their technique and developed a method in which corn waste is treated with an alkaline sodium sulfate solution to produce an additive of viscous compounds [12][13][14][15][16].
The technology of production of alkaline additive is carried out by adding an alkaline solution with a mass ratio of 1:15 or 1:20 of alkaline solution and sodium oxide to corn waste, crushed to 3-4 cm.It is shown that lightweight concretes based on corn waste and slag-alkali binder with complex additive SSPhSFAP (consisting of soda-sulfate mixture, phosphorus slag, fly ash and Portland cement clinker) have increased strength.So, the compressive strength was 2.9 MPa and 2.0 MPa, respectively, after 56 days after curing (Figure 2).The degree of hydration of minerals in the composition of binder with SSPhSFAP in slag-alkali lightweight concrete is high.
To determine the effect of cellulosic organic aggregate based on corn waste on the physical and mechanical properties of the developed slag-alkali lightweight concrete, studies were carried out by mixing the binder with a two-day aqueous extract of crushed corn waste.The active component of such binders might be in the form of Portland cement clinker combined with sodium chloride, sodium sulfate and sodium carbonate salts.
The main role in the curing process of the investigated slag-alkali binder compositions is played by sodium sulfate and sodium carbonate of the alkaline component of the soda-sulfate mixture, which is due to its chemical composition; therefore, the neoformations were studied in systems based on each of these components.
The control of the process of structure formation in the slag-alkali binder system by introduction of rapidly hydrating cement mineral additive, and the study of the composition on the basis of these sodium compounds, characterized, as is known, by low activity in relation to electrothermal phosphorus slag in the conditions of natural hardening, were carried out at steaming with the addition of Portland cement clinker.
The data of X-ray phase analysis of light concrete specimens based on corn waste with mixed admixtures consisting of soda-sulfate mixture, phosphorus slag, fly ash and 7 % of Portland cement clinker from the weight of slag showed that the reflexes observed on the X-ray diagram with (4.82; 2.60; 1.918; 1.681; 1.443 A0) indicate the presence of low-basic tobermorite group calcium hydrosilicate (figure 3).
This points out that the specimens with additive have significantly more calcium hydroxide than those without additive, and the hydration process is much more intense.It has been experimentally established that pretreatment of organic vegetable raw materials with alkaline solution for the removal of hydrolyzable and water-soluble substances improves the quality of lightweight concrete based on corn waste.The study also showed that increasing the particle size of corn waste decreases the average density of lightweight concrete and increases the strength of concrete.

Conclusions
The analysis of the use of concrete and binders shows that lightweight concrete on organic aggregates with high thermal insulation and physical and mechanical properties is the most effective in sharply continental climatic regions of Russia and Kazakhstan.The possibility of using corn waste as an aggregate of lightweight concrete is demonstrated.Also, in the regions of Russia and Kazakhstan there is a large amount of industrial waste slag and sludge, which is used in mixed binders.
It is established that the introduction of a composite additive consisting of soda sulfate mixture, phosphorus slag, fly ash and Portland cement clinker into the composition of slag-alkali lightweight concrete based on corn waste) leads to an increase in its compressive strength up to 2.7-3.0MPa.It was found that slag-alkali binders with additives do not reduce their strength properties in the presence of water-extractable materials of corn waste.
The dynamics of strength increase of slag-alkali binders with addition of phosphorus slag, fly ash, Portland cement clinker and liquid glass with soda-sulfate mixtures in the composition of lightweight concrete with corn waste has been established.The maximum additive content is 1.1% of the slag binder weight.The neutralizer consumption depends on the specific surface area of the organic filler, and the hardener consumption depends on the amount of slag-alkali binder and neutralizer.

Fig. 2 .
Fig. 2. Strength improvement of lightweight concrete based on corn waste slag with various additives: 1 -lightweight concretes based on corn waste on the basis of Portland cement clinker with additives of fly ash; 2 -lightweight concretes based on corn waste on the basis of slag-alkali binders with fly ash additives; 3 -lightweight concretes based on corn waste slag-alkali binder compositions with additives of soda-sulfate mixture; 4 -lightweight concrete based on corn waste and slag-alkali binders with gypsum additives

Fig. 3 .
Fig. 3. X-ray radiography of concrete samples based on corn waste with additives consisting of soda-sulfate mixture, phosphorus slag, fly ash and 7 % of Portland cement clinker from slag weight