The paper deals with the effectiveness of various types of polymers (naphthalene formaldehyde, polycarboxylate, and lignosulfonate) as superplasticizers of concrete mixtures based on low-clinker slag Portland cement. Using the mathematical planning experimental method and statistical models of water demand of concrete mixtures with polymer superplasticizers, as well as concrete strength at different ages and under different curing conditions (normal curing and after steaming) were obtained. According to the models, the superplasticizer’s water-reducing effect and relative change in concrete strength were obtained. The proposed criterion for evaluating the effectiveness and compatibility of superplasticizers with cement takes into account the water-reducing effect of the superplasticizer and the corresponding relative change in concrete strength. The results demonstrate that the use of the investigated superplasticizer types and low-clinker slag Portland cement allows for achieving a significant increase in concrete strength. The effective contents of various polymer types, which allow the achieving of concrete strengths from 50 MPa to 80 Mpa, has been found.

This article presents a modified formula for determining the bond stress which depends on the strength of the concrete. The strength of the connection between t

The article discusses the possibility of improving the properties of concrete made with composite ash-containing cement (CC) by introducing complex chemical additives. The pozzolanic activity of CC and its degree of hydration increases with the increasing dispersion of cement resulting from the introduction of a complex additive in the form of a polyfunctional modifier (PFM) during grinding, including a grinding intensifier-propylene glycol and a superplasticizer. The analysis of mathematical models of water demand and strength of concrete made with the PFM additive showed that a significant reduction in water demand and an increase in the strength of concrete based on the ash-containing CC is possible with the introduction of the PFM additive. For concrete based on CC with the addition of PFM, it has been demonstrated that it is possible to design concrete mixes on the basis of the obtained models. Relevant examples are provided.

The paper presents the results of a study focused on technological parameters that ensure the effectiveness of using concrete powders obtained from crushed concrete waste as an active mineral additive in construction mixtures used for 3D printing. The efficiency of using a complex polyfunctional additive to cement pastes and mortars based on it is experimentally demonstrated. This additive includes a naphthalene–formaldehyde-based superplasticizer and a water-retaining additive, hydroxyethyl methylcellulose. Using the mathematical experiment planning methodology, polynomial models of the cement pastes and mortars’ mechanical properties were obtained. The models showed a positive effect of the complex additive on the cement pastes’ normal consistency and viscosity. Additionally, the results of the study demonstrate the possibility of regulating the cement pastes’ setting time and the plastic strength of mortars based on them using a complex additive. Analysis of the experimental–statistical models shows that using the complex additive allows regulation of water separation as well as the compressive and flexural strength of cement–sand mortars based on the investigated cement pastes within the required limits. Improving the key properties of building mixtures containing crushed concrete waste for 3D printing using complex polyfunctional modifier additives opens up new opportunities for increasing their economic and environmental efficiency.

The article proposes a method that considers the parameters of heat and moisture treatment of concrete when designing its composition. Based on the analysis of experimental data, formulas are proposed that allow taking into account the type and characteristics of cement, the characteristics of aggregates, the effect of temperature and duration of steaming, and the water-cement ratio. Graphs and nomograms have been obtained, which makes it possible to simplify the calculation procedure according to the proposed method. Typical numerical examples of the application of this technique are given.

Анотація Наведено результати досліджень властивостей самоущільнювальних дрібнозернистих бетонів з використанням поліфункціонального модифікатора. Показано, що при оптимальному складі та вмісті такого модифікатора, що включає в себе полівінілацетатну дисперсію та суперпластифікатор, стає можливим суттєво покращити властивості самоущільнювальних бетонів.