MATEC Web of Conferences, open access proceedings in Materials science, Engineering and Chemistry

A thermodynamic analysis of the reactions of calcium chloride and calcium nitrate with tricalcium aluminate when used as a hardening accelerator for portland cement, as well as decomposition reactions of calcium hydrochloraluminate (CHChA) and calcium hydronitroalyuminate (CHNA) formed during the hardening was performed. The conditions of stable existence of CHChA and CHNA in the cement matrix were established.

The influence of the alkaline component on the physico-mechanical properties and the structure of the clinkerless waterproof composition on the basis of Kryvyi Rih blast furnace slag and an alkaline component – sodium hydroxide – have been investigated. High and very high correlation between the compressive strength f of the composition and the alkali – sodium hydroxide – strength A/S has been established. The dependence f on A/S has an extreme wave-like pattern with maxima at A/S = 1.5% and 15-20%, which is explained by the formation of one and two series of hydration products between slag particles similarly to Portland cement-based compositions. It has been established that the hydration products of the composition are predominantly gel-like one, such as hydrosilicate gel and zeolite-like sodium calcium hydroalumosilicates; fewer crystalline hydration products include prismatic and needle-like crystals of complex salts of aluminate phases. The pore size in the composition structure mostly does not exceed 2 microns, although single pores up to 10 microns in size also occur.

Cement-based penetrating waterproof compounds compact the concrete structure due to penetration into the microcracks, pores and capillaries of slightly soluble crystalline hydrates. The coatings made from them do have some drawbacks such as low tensile strength and shrinkage, which may lead to cracks and reduce impermeability. Dispersed fiber reinforcement allows improving these parameters. The surface electric properties of glass fibers and polyester fiber were studied; their ability to be a substrate for the growth of crystalline hydrates was studied; X-ray phase and thermal analysis of cement hydration products with a complex chemical additive providing penetrating action were carried out; electron microscopic studies of the contact zone between fibers and crystalline hydrates were carried out; experimental studies of the dependence of the composition physical and mechanical and hydrophysical properties on the additive and fiber content were carried out. It was found that a dense liner of crystalline hydrates and hydrosilicate gel is formed around the glass fiber and polyester fiber with a silicone dressing size. Between the crystalline hydrates and the fiber surface, strong electro-heterogeneous contacts are formed, which provide the high physical and mechanical properties of the composite. The amount of the complex chemical additive and polyester fiber that provides the maximum strength and minimum water absorption of the composition is determined experimentally.

The paper presents a computer modelling technique for modernization of bridgework operations by building-up a mounted reinforced concrete slab. It implements the technique of the evolutionary transformation of a model in one calculation cycle with redistribution of forces between the elements of the built-up section, and consideration of the impact of elastoplastic and rheological properties of the materials. Consideration of the concrete creep implies the application of the generalized kinetic curve of prolonged deformation and phenomenological deformation development equations based on the colloid-chemical concept of the prolonged concrete deformation mechanism. The creep control was implemented through new structural coefficients which determined the structure of matrix interlayers between the sand grains, and mortar between the crushed stone grains. The technique proposed was realized in the program complex “LIRA-SAPR” based on the building information modelling (BIM) and the finite element method (FEM). The multistage modelling technique was shown by an example of calculation of a motorway bridge slab span within the transport structures under modernization along the Lev Landau Avenue in Kharkiv (Ukraine).

MATEC Web of Conferences, open access proceedings in Materials science, Engineering and Chemistry