The Influence of Composition and Recipe Dosage on the Strength Characteristics of New Geopolymer Concrete with the Use of Stone Flour

Currently, considering global trends and challenges, as well as the UN sustainable development goals and the ESG plan, the development of geopolymer binders for the production of geopolymer concrete has become an urgent area of construction science. This study aimed to reveal the influence of the component composition and recipe dosage on the characteristics of fine-grained geopolymer concrete with the use of stone flour. Eleven compositions of geopolymer fine-grained concrete were made from which samples of the mixture were obtained for testing at the beginning and end of setting and models in the form of beams and cubes for testing the compressive strength tensile strength in bending. It was found that the considered types of stone flour can be successfully used as an additive in the manufacture of geopolymer concrete. An analysis of the setting time measurements showed that stone flour could accelerate the hardening of the geopolymer composite. It was found that the addition of stone waste significantly improves the compressive strength of geopolymers in comparison with a geopolymer composite containing only quartz sand. The maximum compressive strength of 52.2 MPa and the tensile strength in bending of 6.7 MPa provide the introduction of potassium feldspar in an amount of 15% of the binder mass. Microstructural analysis of the geopolymer composite was carried out, confirming the effectiveness of the recipe techniques implemented in this study.

NON-DESTRUCTIVE CONTROL OF CERAMICS BY THE RESULTS OF MEASURING ITS PERMITTIVITY IN THE MICROWAVE RANGE AND AT CONSTANT VOLTAGE

The results of evaluating the mechanical strength characteristics of ceramic samples by a non-destructive method based on measuring their permittivity are considered. In this case, measurements of the permittivity were carried out both in the microwave range on an 8-mm interferometer and in a constant electric field. Measurements in a constant electric field demonstrated the best information content and correlation with the ultimate strength in bending of the studied samples.

Durability of Modified Fiber Concrete for Rigid Pavements

Modified concretes and fiber concretes for rigid pavements have been investigated. Four-factor experiment was conducted. The amount of Portland cement, polypropylene fiber, metakaolin and polycarboxylate superplasticizer varied in the experiment. All mixtures had the same mobility S2. The active mineral additive metakaolin increases the compressive strength of concrete and its tensile strength in bending. The amount of metakaolin at the level of 15.20 kg/m3 is rational. Due to a decrease in W/C with an increase in the amount of superplasticizer Coral ExpertSuid-5 to 0.9.1%, the compressive strength of concrete increases by 5.7 MPa, the tensile strength in bending increases by 0.5.0.6 MPa. Due to the introduction of polypropylene fiber, the tensile strength of concrete in bending increases by 0.6.0.9 MPa, the frost resistance of concrete increases by 50 cycles. Due to the use of a rational amount of superplasticizer and metakaolin, the frost resistance of concretes and fiber concretes concrete increases by 50-100 cycles. The use of a rational amount of modifiers and fiber reduces the abrasion of concretes by 40.45%. The developed modified fiber concretes of rigid pavements, depending on the amount of Portland cement, have compressive strength from 55 MPa to 70 MPa, tensile strength in bending from 8 MPa to 9.5 MPa, frost resistance from F350 to F450, abrasion from 0.30 to 0.40 g/cm2. Such strength, frost resistance and abrasion resistance allow the use of fiber concretes in pavements with the greatest load and ensures high durability of the material and corresponds to the directions and tasks of the state scientific and technical program “National Transport Strategy of Ukraine for the period up to 2030”

Supersulfated Cement Applied to Produce Lightweight Concrete

The physical and mechanical characteristics of expanded-clay lightweight concrete based on a supersulfated binder in comparison with lightweight concrete based on ordinary Portland cement were studied. In replacing CEM 32.5 with a supersulfated binder of 6000 cm2/g specific surface, one can increase the tensile strength in bending up to 20% and can increase the ratio of the tensile strength in bending to the compressive strength that indicates the crack resistance increase of concrete. Compressive strengths at the age of 28 days were equal to 17.0 MPa and 16.6 MPa for the supersulfated binder of 3500 cm2/g specific surface and CEM 32.5, respectively. Shrinkage deformation of hardening concrete, indicators of fracture toughness, frost resistance, and thermal conductivity were determined during the experimental works. The coefficient of thermal conductivity decreased up to 12% compared to the use of CEM 32.5. An enhancement in concrete properties was associated with the increase of supersulfated binder fineness.

Influence of alloying elements and heat treatment on the mechanical properties of chromium cast iron

The results of experimental studies to determine the effect of alloying and heat treatment on the mechanical properties of the high-chromium cast iron are described. When alloying the melt with nickel, molybdenum and manganese, as well as during heat treatment by quenching, specific wear, tensile strength in bending of the obtained samples, their hardness and microhardness were studied. A comparative analysis of the influence of alloying elements and heat treatment methods has been performed. When alloying Ni, Mo, and Mn, cast specimens that have not undergone heat treatment have the highest specific wear. It was established that the hardened Ni alloyed samples have the greatest bending strength. It was found that cast samples that were not subjected to heat treatment have much lower hardness and microhardness. The approximate composition of chromium cast iron was determined for further studies to increase its wear resistance. The research results are used in the manufacturing process of parts for crushing and grinding equipment.

The efficiency of plasticizing surfactants in alkali-activated cement mortars and concretes

Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar 6.6 /30.6 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures).

Evaluation of Selected Physicomechanical Properties of SFRC according to Different Standards

Steel fiber reinforced concretes are currently very popular, especially in the construction of industrial floors of warehouses and other halls with relatively large floor areas. However, it is important to mention that despite the rapid development of steel fiber reinforced concretes, the standards and regulations for their designing and testing have not been unified yet. This paper presents findings about the physicomechanical parameters of the steel fiber reinforced concretes manufactured by adding steel fibers into the truck mixer on the building site. The experimentally obtained results from the performed tests of tensile strength in bending according to various procedures are compared, and the suitability of the methods used is assessed according to these procedures.

Bending strength and phase composition of cement stone subjected to loading at an early stage

The article deals with the results of comparative tests of the phase composition of cement stone distinguished by strength under bending and compression. The comparison has been made between samples subjected to early loading and control samples. An increase in tensile strength in bending of samples subjected to early loading was recorded. The difference in compressive strengths does not exceed 5%. X-ray phase analysis indicates amorphous phase increase with the growth of strength properties, which is manifested in increased intensity of the amorphous phase arc in the X-ray diffraction pattern. The highest peak of the curve corresponds to the maximum flexural strength of the entire row of samples. Among the samples subjected to early loading, the peak intensity of the group of crystal tobermorites with interplanar distances 11.5-11.3Å and 12.5Å appeared to be higher than the intensity of the control samples. It was proposed that the amorphous structure affects the increase in tensile strength in bending of cement stone subjected to early loading.

CYCLIC TEMPERATURE LOADING RESIDUAL FLEXURAL STRENGHT OF REFRACTORY SLABS

This paper describes the effect of cyclic elevated temperature loading on refractory slabs made from high performance, fibre reinforced cement composite. Slabs were produced from aluminous cement-based composites, reinforced by different dosages of basalt fibres. The composite investigated in this study had self-compacting characteristics. The slabs used were exposed to different thermal loading – 600 °C, 1000 °C, six times applied 600 °C and 1000 °C. Then, flexural strength was investigated in all groups of slabs, including group reference slabs with no thermal loading. The results show that the appropriate combination of aluminous cement, natural basalt aggregate, fine filler and basalt fibres in dosage 1.00% of volume is able to successfully resist to cyclic temperature loading. Tensile strength in bending of these slabs (after cyclic temperature loading at 600 °C) achieved 6.0 MPa. It was demonstrated that it is possible to use this composite for high extensive conditions in real industrial conditions.