Concrete Mixtures Research Articles

Active learning on stacked machine learning techniques for predicting compressive strength of alkali-activated ultra-high-performance concrete

AbstractConventional ultra-high performance concrete (UHPC) has excellent development potential. However, a significant quantity of CO2 is produced throughout the cement-making process, which is in contrary to the current worldwide trend of lowering emissions and conserving energy, thus restricting the further advancement of UHPC. Considering climate change and sustainability concerns, cementless, eco-friendly, alkali-activated UHPC (AA-UHPC) materials have recently received considerable attention. Following the emergence of advanced prediction techniques aimed at reducing experimental tools and labor costs, this study provides a comparative study of different methods based on machine learning (ML) algorithms to propose an active learning-based ML model (AL-Stacked ML) for predicting the compressive strength of AA-UHPC. A data-rich framework containing 284 experimental datasets and 18 input parameters was collected. A comprehensive evaluation of the significance of input features that may affect compressive strength of AA-UHPC was performed. Results confirm that AL-Stacked ML-3 with accuracy of 98.9% can be used for different general experimental specimens, which have been tested in this research. Active learning can improve the accuracy up to 4.1% and further enhance the Stacked ML models. In addition, graphical user interface (GUI) was introduced and validated by experimental tests to facilitate comparable prospective studies and predictions.

Effect of sustained elevated temperature on compression and split-tensile properties of concrete made with waste foundry sand

PurposeThe aim of the current study is to inspect the influence of high temperatures on the compressive and split-tensile-strength (STS) of concrete mixtures produced by replacing natural river sand with waste-foundry sand (WFS) at 25%, 50%, 75% and 100%. When the experimental findings and the projected outcomes were compared by IS:456-2000 code equations, the STS results predicted by the suggested mathematical equations exhibit lower variations. It is proposed to employ the presented mathematical formulas to evaluate the STS of concrete cylindrical specimens at higher temperatures.Design/methodology/approachAfter fabricating, concrete mixtures were allowed to cure for 28 days. For the purpose of avoiding explosive spalling during the heating process, concrete samples are taken out from the curing chamber after 28 days and allowed to dry for two days. The manufactured concrete specimen is exposed to 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 600 °C temperatures for a duration of 2 h. After the specimens have cool down to room temperature (RT), the physical test, ultrasonic-pulse-velocity (UPV) test, compressive strength test and STS test are carried out.FindingsWith an increase in WFS content, concrete specimens' residue compressive-strength and STS decreases. The STS of samples declines as the WFS content rises with increase in temperature interval. According to the UPV test, the concrete samples quality is “good” up to 400 °C; after 500 °C, it ranges from “doubtful to poor.” The UPV values of various mixes declined as the temperature increased. Mass losses increase with exposure to greater temperatures and with an increase in the proportions of WFS in concrete specimens. For mixtures MWFS-0, MWFS-1, MWFS-2, MWFS-3 and MWFS-4 (0%, 25%, 50%, 75% and 100% WFS content), no cracks were present on any of the samples below 400 °C. Concrete surfaces start to show cracks whenever the intervals of temperature increase above 400 °C.Originality/valueIn this investigation, WFS elements are totally substituted for natural sand in concrete mixtures. The residue strength properties, including residual compressive strength and residual STS, were found to be lower after exposures to greater temperature when comparisons were made to referral mixtures. When comparing specimens’ compressive strength, higher temperatures have more effects on the STS of samples with higher WFS contents.

Study on the performance of hydrophilic curing agent and environmentally friendly non-pozzolanic filler for the development of self-curing self-compacting concrete.

Self-compacting concrete (SCC) is often used when compaction is difficult, requiring special attention to the curing process. However, traditional curing methods usually fail in practice. Despite taking precise measures to control water evaporation, surface water on vertical structure elements can still be problematic. To address these challenges, this study seeks to investigate the possibility of creating self-curing self-compacting concrete (SCSCC). Since the curing agent used has a significant impact on the production of SCSCC, this study examines the effects of using polyethylene glycol (PEG), a hydrophilic agent, at varying rates of 0.5%, 1%, 1.5%, and 2% on the fresh, hardened, and durability characteristics of the material. Additionally, to improve the sustainability properties of SCSCC, manufactured sand (M-sand) acquired from crushing rocks is used as a filler. Overall, the results indicate that the use of superplasticizer and M-sand is enough to achieve the required flowability for SCC mixtures without requiring specific fillers, and this method is effective in immediately controlling bleeding and segregation while maintaining the necessary compressive strength at all ages. The hardened properties of SCSCC were found to be improved by increasing the PEG content up to 1.5%, with an optimal range of 0.75% superplasticizer. Furthermore, the results demonstrate that the self-cured specimen, cured with PEG, has greater acid resistance than the conventionally cured one.

Preparation of viscosity-reducing polycarboxylate superplasticizer (PCE) and its role in low water-to-cement ratio system

Owing to the low water-cement ratio (less than 0.25) of ultra-high-performance concrete (UHPC) materials, the system exhibits increased viscosity, diminished slurry flow, and challenges in pouring during the construction process, which compromise its workability. Consequently, the development of highly efficient viscosity-reducing polycarboxylate superplasticizer (PCE) is of paramount importance. In this study, we synthesized a series of viscosity-reducing polycarboxylate superplasticizers(JN-PCE) utilizing allyl polyethylene glycol ether (APEG), acrylic acid (AA), and sodium methallyl sulfonate (SMAS) as raw materials through the process of free radical polymerization. Fourier-transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, and energy-dispersive X-ray spectroscopy were employed to characterize the materials. Subsequent evaluations of surface tension, fluidity, adsorption performance, and Marsh time demonstrated that these superplasticizers exhibited commendable dispersion and remarkable viscosity-reducing properties within a low water-cement ratio system. At a water-cement ratio of 0.18, the Marsh time of the JN-type PCE was reduced by 40% while maintaining the same fluidity, thereby underscoring the effective viscosity-reducing capabilities of the synthesized polycarboxylate superplasticizer.

OTIMIZAÇÃO DE MISTURAS DE CONCRETO PARA REDUÇÃO DE CUSTOS COM USO DE POZOLANA

Concrete is the primary source for the development of civil engineering projects. In Brazil, its use reaches approximately 40 million cubic meters per year. As a result, concrete production is a central element in civil engineering, being used in a wide range of applications, from foundations to large structures. However, the costs associated with concrete production represent a significant portion of the total costs of a project. Therefore, the search for methods that can reduce these costs without compromising the quality and durability of structures is of utmost importance for the sector. The main objective of this work is to explore effective methods for optimizing concrete mixtures using additives or applying alternative materials in order to guarantee the quality of the product, with the aim of improving its physical-mechanical and economic characteristics. To achieve this goal, the following specific objectives were defined: to analyze the physical and mechanical properties of different concrete formulations, to identify the main factors that influence concrete production costs, to develop optimization models for concrete mixtures based on economic and performance criteria, and to evaluate the technical and economic feasibility of the proposed solutions in case studies. During the development of the research, comprehensive literature reviews were carried out to understand the latest trends and practices related to concrete production. In addition, laboratory experiments were conducted to analyze the physical and mechanical properties of different concrete formulations, taking into account the influence of variables such as type of aggregate and the use of pozzolan as an additive to improve concrete. Based on the data researched and the tests developed, it was possible to present pozzolan as a satisfactory additive for addition to concrete, since it reduces production costs while maintaining the essential properties of concrete, such as compressive strength, durability and workability. And because it is a more sustainable material, it reduces environmental damage.

High-Performance Concrete from Rubber and Shell Waste Materials: Experimental and Computational Analysis

Waste and its environmental impact have driven the search for sustainable solutions across various industries, including construction. This study explores the incorporation of solid waste in the production of eco-friendly structural concrete, aiming to reduce pollution and promote ecological and sustainable construction practices. In this context, two types of eco-friendly concrete were produced using marine shells and recycled rubber as waste materials and compared with conventional concrete through experimental and computational approaches. The results demonstrated that the concrete with marine shells achieved a compressive strength of 32.4 MPa, 26.5% higher than conventional concrete, and a 1% reduction in weight. In contrast, the recycled rubber concrete exhibited a compressive strength of 22.5 MPa, with a 2 MPa decrease compared to conventional concrete, but a 4.3% reduction in density. Computational analysis revealed that porosity affects Young’s modulus, directly resulting in a reduction in the maximum achievable strength. This work demonstrates that it is feasible to produce eco-friendly structural concrete through the proper integration of industrial waste, contributing to decarbonization and waste valorization.

The physical and mechanical consequences of incorporating industrial residues into mortar and concrete mixtures for eco-friendly marine constructions

The physical and mechanical consequences of incorporating industrial residues into mortar and concrete mixtures for eco-friendly marine constructions

Effect of Super Retarder on Recycled Water and Concrete Properties of Waste Slurry in Mixing Plant

A large amount of waste slurry water will be generated in the production process of concrete mixing plant, due to the complex composition of waste slurry water, if it is not handled in time when stored, serious coagulation will occur, which will accelerate the loss of equipment and reduce the utilization rate. In this paper, a super retarder suitable for waste slurry recycled water from concrete mixing plant was prepared using composite technology. The waste slurry recycled water mixed with super retarding agent was characterized by using microscopic testing means XRD, TG and DTG. The waste slurry recycled water mixed with super retarding agent was used to replace tap water in the production of concrete, and its effect on the workability and mechanical properties of concrete was investigated. It was found that the compounding of Butane 2-phospho-1,2,4-tricarboxylic acid (PBTCA) with Reclaimed water treatment agent (ACS) resulted in a setting time of 64 h for 10% concentration of recycled water, with optimal retarding effect. When PBTCA:ACS was 1:20, mixed at 1.5% of the mass of recycled water, the 1 h slump of concrete had no loss, the loss of extension was 15 mm, the 7 days compressive strength was increased by 3.5 MPa, and the 28 days compressive strength was increased by 3.0 MPa. The microscopic results showed that the use of ACS and PBTCA does not affect the type of cement hydration products, but only affects the the rate of hydration product generation.

A numerical investigation of the structural behavior of reinforced concrete beams fully or partially encased with UHPC layers in flexure

Weakness in the structural facilities appears due to design faults, poor construction, usage change, maintenance lack, material defects, and environmental conditions. Therefore, strengthening structures becomes necessary for deteriorated concrete and enhancing aging concrete elements to achieve satisfactory performance perfectly. This study numerically investigated the structural behavior of conventional concrete beams reinforced with Ultra-High Performance Concrete (UHPC) layers on different sides. The arrangement of UHPC layers, bonding method between traditional concrete and UHPC, layer thickness, and reinforcement ratio were examined using Abaqus software. The interface between the UHPC layer and conventional concrete sustains compressive, tensile, and shear stresses, which cause weak resistance to the stresses at the contact surfaces. Therefore, the simulation of contact face in Abaqus needs a proper numerical model relying on practical methods. However, using the bonding models available in Abaqus is crucial for reaching logical results comparable to the practical ones. The practical bonding approaches are highly consequential, such as roughening surfaces by sandblasting to attain a firm connection between the contact surfaces, which permits using a surface-based tie constraint for simulation. Further, epoxy resin conducts as a thin coating between contact surfaces, making it possible to simulate via a cohesive surface. The results proved that increasing the area encased by the UHPC layer improves load capacity further and reduces the deflection at the maximum load. Surrounding the beam on whole sides with a UHPC raises load capacity by 108 % and reduces deflection by 46 %. Adding a UHPC layer to the beam delays crack initiation and reduces their number and spacing. Increasing the UHPC layer thickness or reinforcement ratio enhances the load capacity of the beam at cracking and the ultimate state.

Enhancing Quality Control in the Mix Design of High-Strength Concrete Using a Capacity-Based Approach

The mix design of concrete is an important aspect that affects its strength and durability. This paper aims to revisit the existing mix design method given in IS 10262:2019 through a capacity-based approach. The approach involves identifying the possible failure modes in concrete and eliminating the undesirable ones leading to significant reduction in dispersion. This is accomplished by utilizing coarse aggregates that meet a specific minimum strength requirement or threshold (e.g., ~ 77 MPa for M95 grade of concrete), which is determined through a priori estimating the cohesion and friction angle of the concrete. The methodology to estimate the cohesion and friction angle from a single unconfined compression test is proposed based on the Mohr–Coulomb theory and using the orientation of failure plane of fractured specimen as a supplemental information from the same experiment. This paper also offers a simple and approximate test procedure to estimate the aggregate's compressive strength (~ 106 MPa in this mix design) reasonably which is essential for the capacity-based mix design. An experimental programme is also carried out to design the concrete mix using the proposed capacity-based approach. The results indicate that M95 concrete is achieved with a low standard deviation and coefficient of variation (~ 3%), falling in class of excellent quality control as per ACI 214R-11. This quality control is crucial in seismic structural design as variations in concrete strength is likely to negate the underlying principle of strong column–weak beam philosophy resulting in the triggering of undesirable shear modes of failure.

Experimental Study On Self-Compacting Concrete Mix Design By Using Yucca Zeolite

This report aims to present the experimental investigation on mix proportioning of normal concrete and self-compacting concrete with yucca zeolite. The study area comprises of ordinary portland cement of grade 53,mix proportioning of normal concrete for grade of concrete M40, M30 and M20 whereas mix proportioning for self-compacting concrete for grade of concrete M40, M30 ,M20.The parameters considered are cement content, Water cement ratio i.e. for normal concrete 0.4, 0.42, 0.45 and for self-compacting concrete 0.62, 0.44, 0.43 respectively. To reduce the risk of shrinkage, frost attack and corrosion of concrete, yucca zeolite as a mineral admixture and to increase the bond strength techno plast S 300 as a super plasticizer is added. The responses of material testing, normal concrete tests that includes slump flow test and compressive strength test recorded. Also, tests on self-compacting concrete recorded from slump flow test, J ring test, V funnel test, L box test, U box test, Rheological parameters, Compressive strength at 7 and 28 days. The various properties of SCC are ascertained with the IS code 1199:2018 [part 6] IS code 456:2000, IS code 10262:2019.

Smart Sensor Placement For Thermal Monitoring Of Concrete

Structural health monitoring (SHM) has become an inevitable part in a life span of a structure due to its potential to ensure the public safety and to increase the life span of the structure. Monitoring any kind of structures for various parameters, using wireless smart sensors has gained popularity in recent past. This paper discusses the development of low cost real time wireless smart sensor monitoring system to monitor early age concrete temperature in real time. Temperature of two early age concrete mixes (Mix1, Mix2) were measured in real time for 24 hours by using DS18B20 sensors connected with the Node Mc u, which is an open source IOT platform. Temperature measurements were saved and visualized in real time using Thing Speak TM which is an open IoT online platform with MATLAB analytics. The temperature sensor DS18B20 was selected such that it is suitable to measure temperature readings of the concrete without any interference of the chemical reactions in concrete. Calibration methods and temperature variation with different concrete mixes are also discussed. It could be seen that the wireless temperature monitoring system performed adequately and it can be considered as a better low cost alternative for traditional wired temperature monitoring system.

Effect of Sporosarcina Pasteurii on Rheological and Strength Properties of Bio-Self Compacting Concrete

The study was conducted to evaluate the rheological and strength properties of bio-self compacting concrete. The materials used are cement, fine and coarse aggregates, bacteria (Sporosarcina pasteurii), and superplasticizer. Preliminary tests were conducted on the materials to ascertain its conformity to standard, and a full factorial design of experiment was adopted. The bacteria nutrient was varied at a ratio 1:3 of the bacteria content (i.e. 75% nutrient and 25% bacteria) at 10^5 cell/ml Sporosarcina pasteurii which was added to the fresh concrete at 5-25ml dosage by weight of water at 5ml increment, while the superplasticizer was added into the fresh concrete at 0.2-1.0% at 0.2 % increment by weight of cement which translated to 234 concrete samples. The rheological tests conducted were slump, V-funnel, L-box, and J-ring test, while the concrete strength tests conducted were compressive, flexural, and split tensile strength. Results from the experiment showed that workability of most of the bio-self compacting concrete is very high compared to the control concrete, and are within the range specified by codes, and the 28 days compressive strength of concrete produced by adding 20 – 25 % bacteria and 0.4-0.8% superplasticizer had 28 days compressive strength equal or greater than the control concrete. Also, the 28 days flexural strength of control concrete is significantly higher than flexural strength of all the bio self-compacting concrete, while the split tensile strength of bio self-compacting concrete produced by adding 25% bacteria and 0.4 – 0.8% superplasticizer is higher than the control concrete.

Comparative Study on the Properties of Fresh and Hardened Concrete Using Metakaolin as Partial Replacement

This study examines the impact of metakaolin as a partial substitute for concrete, analyzing fresh and hardened concrete characteristics. We integrated metakaolin, a pozzolanic substance known for its ability to enhance strength and durability, at various replacement ratios (0%, 5%, 10%, 15%, and 20%) to assess its impact on workability, compressive strength, tensile strength, flexural strength, and resistance to chemical aggression. The workability of fresh concrete went down as the metakaolin content went up. On the other hand, as the metakaolin content went up, the compressive strength, flexural strength, and resistance to acid and sulphate attacks all went up in hardened concrete, though the tensile strength went down a little. The results demonstrate that an ideal metakaolin substitution of around 10–15% can provide significant durability advantages without markedly diminishing workability or tensile strength. This work provides a fundamental understanding for engineers to improve the designs of concrete mixes, especially in situations where chemicals are present.

Superabsorbent Polymers for Internal Curing Concrete: An Additional Review on Characteristics, Effects, and Applications

Superabsorbent polymers (SAPs) are a promising admixture that can provide internal curing to freshly cast concrete and enhance concrete properties. Although many reviews have explored aspects of SAPs, the links among SAPs’ chemical and physical properties, internal curing behaviors, concrete performance, and their large-scale applications are often weakly elucidated. This paper provides an additional review of the chemical structures and physical dimensions of SAPs and their effects on the internal curing kinetic behavior as well as on concrete properties, such as workability, strength, and durability. In addition, different approaches to introducing SAP particles into concrete mixtures are also summarized. Case studies on the use of SAPs in the concrete industry are introduced to provide a better understanding of the greatest potential of SAPs in field applications. The results confirm that the utilization of SAPs in concrete mixtures provides multiple benefits such as improved water curing, reduced shrinkage, and enhanced workability. Selecting the appropriate SAPs is crucial and involves considering factors like absorption rate, durability, and stability. However, achieving uniform distribution of dry SAPs in concrete poses challenges. Further research is required to gain a deeper understanding of the impact of SAPs on transport properties and frost durability. Additionally, the absence of a standard makes it difficult to maintain consistent water-to-cement ratios. These findings provide a theoretical foundation for using SAPs to enhance concrete performance while also highlighting future research directions and challenges. In this article, scientists, engineers, and contractors will find a comprehensive explanation encompassing laboratory investigations, field implementation, and relevant guidance.

Impact of plastic waste fiber and treated construction demolition waste on the durability and sustainability of concrete

This study explores the mechanical and durability properties of Plastic-Fibre Reinforced Concrete, incorporating hand-shredded plastic fibers sourced from polyethylene bags and PET bottles. Evaluations, including compressive and split tensile strength tests, were conducted on M40 grade mixes containing plastic fibers and 100% treated Construction and Demolition Waste (CDW), comparing them with conventional concrete. The results demonstrate a significant enhancement in strength properties with the addition of 0.25%, 0.5%, 0.75%, and 1% plastic-fibres, alongside the complete replacement of coarse aggregate with CDW, particularly noticeable at both 7 and 28-day curing ages. Although higher fiber dosages led to a slight reduction in compressive by 7% at the optimum percentage of 0.25% of PE and 0.5% of PET, the flexural strengths and split tensile strength exhibited a proportional increase of 11.7% and 18%. Surface analysis via Scanning Electron Microscopy (SEM) and elemental composition determination using Energy Dispersive Spectroscopy (EDS) revealed minimal fiber damage post-exposure, confirming its efficiency and contribution to higher strength and reduced weight loss in optimum mix. This novel approach combines manually recycled plastic waste as fibers with treated CDW, enhancing concrete properties while promoting sustainability. Sustainability analysis indicates that utilizing 100% CDW and plastic fiber contributes to reduced energy consumption, lower carbon emissions, and economic benefits. These findings underscore the potential of integrating non-degradable plastics into concrete mixtures, combined with treated CDW, offering both environmental sustainability and enhanced performance advantages in construction materials.

An investigation on workability and strength on compression of GPC with addition of different aspect ratio glass fibers

The heating of limestone and other materials to high temperatures to produce Ordinary Portland cement (OPC), a key component in concrete releases of carbon dioxide CO2 which makes the construction industry a notable contributor to greenhouse gas emissions. The search for more sustainable alternatives has led to the exploration of alkali-activated materials as a replacement for OPC. Alkali-activated materials are a class of binders that can be used in concrete production without the need for traditional cement. These materials often include industrial by-products such as fly ash, GGBFS (sometimes also called GGBS) (Ground Granulated Blast Furnace Slag), and other waste materials. The development and adoption of alkali-activated materials represent a promising avenue for reducing the environmental impact of the construction industry. On-going research and collaboration are crucial to addressing technical challenges and promoting the widespread use of these alternative binders. The exploration and utilization of alternative materials such as GGBFS, fly ash, and geopolymer concrete play a crucial role in mitigating the environmental impact of the construction industry, particularly in terms of reducing CO2 emissions and utilizing industrial by-products effectively. A good concrete mix is obtained from combination of different size of aggregates. Addition of fibers plays a crucial role in enhancing the tensile strength of concrete. Similar synergy of addition of different aspect ratio of optimum dosages fibers as of different size of aggregates may improve strength and ductility of concrete. Short fibres can stop the propagation of micro-cracks with enhancement of toughness, and long fibres can stop the propagation of macro-cracks. From the aforementioned perspective, it is preferable to add the same volume of fibre with a different aspect ratio to improve the pre- and post-cracking performance of concrete. It also aids in boosting maximal strength.This study aims in preparing geopolymer concrete with graded glass fibres in order to investigate improvement the strength in compression and workability.

Optimizing sustainable concrete mixes with recycled aggregate and Portland slag cement for reducing environmental impact

Concrete is the world’s most extensively manufactured material, with the integration of recycled materials becoming crucial for sustainable construction. This study investigates the mechanical properties of concrete mixes containing Recycled Aggregates (RA) and Portland Slag Cement (PSC) to understand their suitability for sustainable construction applications. Utilizing normal-strength concrete with a compressive strength of 35 MPa and a 0.45 water-to-cement ratio, fifteen mix designs were tested, varying RA and PSC replacement levels from 0 to 100% and 0% to 50%, respectively. Comprehensive mechanical testing, including compressive and tensile strength assessments at 7 and 28 days, alongside modulus of elasticity and stress–strain curve evaluations, was conducted. The results reveal that full replacement of Natural Aggregate (NA) with RA decreased compressive strength by 10% and modulus of elasticity by 20%. However, a partial replacement of 25% of Ordinary Portland Cement (OPC) with PSC, in the presence of RA, moderated the reduction of compressive strength to 0.92% and increased the modulus of elasticity by 3.7%. The optimum mix, consisting of 75% OPC, 25% PSC, and 50% RA, significantly enhances concrete’s mechanical properties, recommending it for reinforced concrete applications due to its potential environmental and structural benefits.

Self-Compacting Mixtures of Fair-Faced Concrete Based on GGBFS and a Multicomponent Chemical Admixture—Technological and Rheological Properties

The use of superplasticizers in a self-compacting concrete mix without the addition of a foaming agent in practice leads to a well-known problem associated with increased air entrainment and promotes the formation of harmful large bubbles, high-void content, and ununiform appearance. This paper presents research on the properties of cement paste consisting of Ordinary Portland Cement (OPC), powder based on ground granulated blast furnace slag (GBBS), and superplasticizer. The methodology of this study was the estimation of flow diameter and flow time, as well as the evaluation of the rheological characteristics. The influence of ground granulated blast furnace slag and polycarboxylate plasticizer on the flowability and viscosity of cement paste was studied. The effect of superplasticizer (SP) based on polycarboxylate esters (PCE) anti-foaming agent (AFA) based on a glycol ester and air-entraining admixture (AEA) based on an amphoteric surfactant on flowability, viscosity, rheological properties and the strength of the cement paste was evaluated. It was found that the increase of slag content in cement paste (25%) with the presence of superplasticizer (0.64%) significantly changes the flowability and viscosity. It was stated that the addition of 0.04% anti-foaming agents increases flowability (20%) and reduces viscosity (44%) of cement paste. It was stated that the addition of small dosages of glycol ester-based anti-foaming agent (0.02 and 0.04%) significantly changes the rheological properties, decreases the shear yield stress by 2.1–2.8 times, the plastic viscosity by 2.4–2.6 times and apparent viscosity 1.6–2.5 times, improves the compressive strength at the age of 1 and 7 days by 2.5 and 1.4 times, respectively. The addition of air-entraining admixture led to a decrease in the plastic viscosity by 1.2–1.4 times. It was stated that the presence of air-entraining admixture assists in increasing the apparent viscosity by 1.7–2.4 times. It was shown that the presence of complex admixtures of various origins, purposes, and mechanisms of action would assist in predicting the behavior of concrete mixtures under the conditions of the building site and reduce the consumption of polycarboxylate esters due to the enhancing plasticizing effect of anti-foaming agent and air-entraining admixture.

Rheological Characteristics of Concrete Mixtures Modified with Urease Additives

Statement of the problem. Rheological characteristics of concrete samples made with the use of various bioadditives are studied. Results. The results of experimental studies of the rheological properties of concrete, taking into account the effect of dietary supplements based on the following strains of bacteria B.subtilis, Ps.aeruginosa, with urease activity, are presented. Conclusions. The values of the cone sediment of concrete mixtures made using various grades of Portland cement were obtained, the values of conditional viscosity were also established, and the limiting shear stress and compressive strength of the obtained concrete cube samples made using urease bioadditives were determined. It was found that the use of dietary supplements leads to a decrease in the conditional viscosity of the mixture by 2 times, as well as to an increase in compressive strength by at least 15 %. Thus, it has been established that bioadditives improve the quality of the bond between the components of concrete, making it more durable and resistant to loads, as well as its rheological characteristics.