Compressive Strength Class Research Articles

ASSESSMENT AND FORECASTING MAXIMUM CARBONIZATION OF CONCRETE

The article substantiates the need to study the carbonation of concrete and evaluate the maximum carbonization of it. The basic equation of prediction of change in time by concrete cross section of carbonate component of cement-sand fraction of concrete is given. An expression is proposed for estimating the limit value of concrete carbonation (PVC). PVC from concrete composition (amount of used cement) for concrete without additives, compressive strength classes С8/10–С50/60, mixture compositions, grades for ease of laying P1...P5 and G1...G4 for each class of concrete in terms of compressive strength and different tempering strength of concrete was investigated. The obtained PVC values were analyzed. Dependencies of PVC change on the amount of used cement for any class of concrete in terms of compressive strength and different grades of mixtures in terms of ease of laying, as well as dependence of change of limit value of carbonization of non-addition concrete on the amount of used cement for different tempering strength of concrete and grades of mixtures in terms of ease of laying are obtained.

Моделирование напряженного состояния и определение прочностных характеристик материалов несущих конструкций промышленного цеха

The paper presents a part of the results of a full-scale inspection of the molding shop of an industrial enterprise. The results of tests of masonry materials of the shop's enclosing walls by the shock pulse method using the ONIKS 2.5 device are presented. As a result, it was found that the grade for the compressive strength of the ceramic bricks of the walls corresponds to M100, and the grade of the masonry cement-sand mortar of the walls of the building corresponds to M50. The results of concrete testing by the non-destructive method of testing the strength using the DigiShmidt 2000 device were presented. As a result, it was established that the compressive strength class of concrete in reinforced concrete slabs of the pavement corresponds to B10, in reinforced concrete beams of the pavement - B40, in reinforced concrete crane beams of the covering - B15, in reinforced concrete columns of the building - B15. Instrumental studies were carried out using non-destructive testing methods, and verification calculations were carried out using a computer. The results of the verification calculations carried out according to the proposed method showed the sufficient bearing capacity of the roof beams, columns and foundations of the workshop building under the full design load. Based on the results of the survey, a verification calculation of the workshop frame was carried out. In general, the calculation showed sufficient strength of the entire load-bearing structures of an industrial building.

EFFECT OF POLYCARBOXYLATE SUPERPLASTICIZERS ON THE PROPERTIES OF READY-MIX CONCRETE

The article analyzes the experience of using Portland limestone cement for the production of ready-mixed concretes. It is shown that polycarboxylate superplasticizers (PCE) play a decisive role in providing required technological and construction-technical properties of concrete. The data show that the most effective PCEs for maintaining the workability of the concrete mixture over time and obtaining the required strength class of concrete are РСЕ based on modified acrylic polymers. It was found that polycarboxylate superplasticizers provide a significant water-reducing effect (ΔW/C = 38%) and was achieved compressive strength class C45/55. It is shown that such concretes are characterized by its rapid strength development (fcm2/fcm28=0.54). The ready-mix concrete with PCE was used for concreting foundations of wind turbines on the wind power plant with provide the technological properties and of reduce CO2 emissions.

Modelling of Modulus of Elasticity of Low-Calcium-Based Geopolymer Concrete Using Regression Analysis

Despite the unremitting efforts to model the modulus of elasticity of low-calcium-based geopolymer concrete, the state-of-the-art models need much improvement to reduce the error signals and increase the reliability. This study represents a comprehensive regression analysis to model the modulus of elasticity of low-calcium-based geopolymer concrete in terms of its compressive strength. The proposed model’s assumptions are based on taking into account the chemical composition and compressive strength class and considering the normal density of concrete. The modelling is based on 67 different mix-design samples collected from peer-reviewed literature, which are divided into two groups. The first group consists of 59 samples that are used to construct the proposed model, while the second group consists of 8 samples that are used to test the validity of the proposed model. The analysis showed that the proposed model gives the root mean squared error value (RMSE) of 3.122 GPa and the mean absolute percentage error value (MAPE) of 15.0%. Therefore, the proposed model gives 41% and 52.2% reductions in RMSE and MAPE, respectively, from the state-of-the-art model in the literature. Furthermore, other statistical parameters to evaluate the goodness of fitness of the proposed model have been considered, such as the relative root mean squared error (RRMSE) (15.5%), the coefficient of determination (R-squared) (0.773), and the coefficient of correlation (R) (0.88); all of which indicated that the goodness of fitness is good and the proposed model has a high correlation to the actual values. Applying the proposed model in future applications will help reduce the time and cost of geopolymer production, as the proposed model has significantly reduced the error signals.

Experimental Study on the Physical and Mechanical Characteristics of Roller Compacted Concrete Made with Recycled Aggregates

A huge volume of waste is generated by natural and human-made disasters and by rapid urbanization that leads to the demolition of structures reaching the end of their service life. Using recycled aggregates in concrete producing reduces environmental pollution by decreasing the disposal of this waste material in landfills and preserving unreasonable exploitation of natural resources. This manuscript presents the results of an experimental program aiming to study the effect of recycled aggregates on the physical and the mechanical properties of roller compacted concrete (RCC). A Dreux–Gorisse mix design method together with the modified proctor test were adopted to prepare a reference mixture with natural aggregates with three derived mixtures where coarse aggregates were replaced by 50%, 70%, and 100% of recycled aggregates. The physical properties of RCC were evaluated by means of water absorption and gas permeability tests while the mechanical properties were evaluated using compressive, tensile splitting and 3-point flexural tests. The results of physical tests showed that both water absorption ability and gas permeability increase proportionally with the replacement ratios. The results of the mechanical tests showed that the compressive strength class was approximately constant for all developed mixtures at the age of 28 days. For a substitution ratio of 100%, a drop in the compressive strength of only 6% was recorded. The reduction in the tensile and flexural strength was more pronounced than the compressive strength and was about 10% for the mixture of 100% recycled aggregates. It was found that the strength increases with time, and it can be estimated at any age using the analytical models adopted for conventional hydraulic concretes. Based on the obtained results, it was concluded that recycled aggregates up to 50% don’t negatively affect the physical and mechanical properties of RCC.

Анализ дефектов несущих конструкций производственного здания

All buildings with a significant service life must be regularly surveyed. This work analyzes the results of the inspection of the building of the compressor shop KC-1. Analysis of the design documentation and the results of measurement work showed that structurally the building has overall dimensions in plan along the outer axes of 21.0 × 72.0 meters. The height of the building is 17.0 meters. The conducted visual examination showed the presence of damages and defects of the third and fourth categories, which requires an instrumental examination. In particular, the need to determine the strength of brickwork and the strength of concrete in structures. The analysis of the results of the instrumental examination showed: the results of testing the wall masonry by the shock pulse method using the ONIKS 2.5 device showed that the compressive strength grade of the silicate brick of the compressor shop walls corresponds to M75 and M125, and ceramic M100. The grade of the masonry mortar for the walls of the compressor shop corresponds to M50 and M75; The results of concrete testing by the non-destructive method of strength control using the DigiShmidt2000 device showed that the compressive strength class of concrete in the reinforced concrete columns of the workshop corresponds to B20, in the girders B25, floor slabs and coating slabs B20. Verification numerical calculations on the computer of the bearing capacity of the building structures of the compressor shop building were performed taking into account the actual static diagrams, sections of elements, strength characteristics of materials established during the survey, and constant loads existing at the date of the survey. Based on the results of the verification calculation of the building structures of the transverse frame of the building, it was found that the bearing capacity of the upper chord of the truss was not provided. The bearing capacity of the building columns when calculating according to the first and second groups of limiting states is provided. In general, the analysis showed that the technical condition of the technical condition of the compressor shop KC-1 is unacceptable.

Rheology, Setting Time, and Compressive Strength of Class F Fly Ash–Based Geopolymer Binder Containing Ordinary Portland Cement

AbstractThis paper investigates the incorporation of ordinary portland cement (OPC) to adjust/improve the workability, setting time, and compressive strength of Class F fly ash (FA)–based geopolyme...

АНАЛИЗ ПРОЧНОСТИ ПРИ ОСЕВОМ РАСТЯЖЕНИИ КЛАДКИ ИЗ ЯЧЕИСТОБЕТОННЫХ БЛОКОВ АВТОКЛАВНОГО ТВЕРДЕНИЯ НА РАЗЛИЧНЫХ РАСТВОРАХ И КЛЕЕВЫХ СОСТАВАХ

The article presents the results of a comparative analysis of the axial tensile strength of masonry made of autoclaved cellular concrete blocks with cement mortars of various grades and polyurethane adhesive compositions of various manufacturers. The tests were carried out on prototypes made of two cubes of 150x150x150 mm glued together. As cellular concrete, blocks of autoclaved hardening of the compressive strength class B1.5, B2.5, B3.5 were used. M200 and M300 cement mortars, "Tytan Professional”, "Technonicol", "Bonolit" and “KUDO” foamed polyurethane glues were used as a binder. The experiment was performed in the Laboratory of the Department of Reinforced Concrete and Masonry Structures of the Moscow State University of Civil Engineering. On the basis of the experiment, the values of the increase in the strength of the masonry under axial tension were obtained depending on the binder.

Improving Marine Concrete Performance Based on Multiple Criteria Using Early Portland Cement and Chemical Superplasticizer Admixture.

This study sought to examine the performance design of concrete mix proportions to ensure chloride resistance and early strength with respect to C35 (35 MPa), which is the minimum compressive strength class of concrete used in a marine environment. For the proposed concrete mixture, C24 (24 MPa) was selected and binders for concrete were manufactured using a blend of OPC (ordinary Portland cement), EPC (early Portland cement), and GGBS (ground granulated blast-furnace slag). The results of the experiment confirmed that the combined use of EPC and GGBS greatly improve the early-strength development and chloride resistance of concrete. An analysis revealed that the time for removal of forms can be reduced by 5–9 h from the aspect of early concrete strength. Moreover, in terms of construction productivity, EPC and GGBS were reduced by up to 16.39 h/cycle compared to other concretes. Regarding economic and environmental impacts, EPC and GGBS were more effective than C35 concrete. This study is significant as its findings help make it possible to examine the most economical concrete mix design in relation to strength development according to the application of EPC, GGBS, and PC-based admixtures.

Mechanical, environmental and economic performance of sustainable Grade 45 concrete with ultrahigh-volume Limestone-Calcined Clay (LCC)

Low-grade calcined clay mixed with limestone powder (Limestone-Calcined Clay, LCC) is a new kind of cement replacement material in the face of the inadequate availability of conventional pozzolans such as fly ash. Because of the high water demand and likely insufficient strength gain of LCC, the information on using more than 50% of LCC in the binder is extremely limited, which hinders using LCC in a higher replacement level to develop greener concrete. This study attempts to address this knowledge gap by producing Grade 45 structural concrete with ultrahigh-volume LCC (UHV-LCC). UHV-LCC mortar mixes with various LCC/binder ratios (50-80%) and water/binder ratios (0.3-0.4) were firstly examined to determine the cementing efficiency factor of LCC. Four Grade 45 UHV-LCC concrete mixes with different LCC/binder ratios (50%, 60%, 70% and 80%) were then designed and demonstrated. With the judicious choice of water/binder ratio, UHV-LCC concrete achieved compressive strength of 33-37 MPa at 3 days, 47-51 MPa at 7 days, 56-58 MPa at 28 days, and 62-64 MPa at 90 days. The flexural strength of UHV-LCC concrete was 2-10% higher than that of plain Portland cement concrete with identical compressive strength class. Additionally, UHV-LCC concrete showed 36.8-44.4% lower total embodied carbon than plain Portland cement concrete, and a higher LCC/binder ratio resulted in lower embodied carbon in Grade 45 concrete. A 5-D representation was used to evaluate different concrete mixes by comprehensively considering the mechanical, environmental, and economic performance. Our findings are useful for the mix design of sustainable concrete with LCC.

Mechanical performance and resistance to carbonation of steel slag reinforced concrete

The use of residues as alternative materials in the production of cement-based composites is significantly growing since it embraces the circular economy concepts. This alternative reduces the demand for natural resources by the construction sector and provides a proper destination for a range of industrial residues. However, the alternative materials must perform properly for safe applications. In this way, the steel slag, a residue of the steel industry, stands out. The steel slag is already applied in some cement-based composites showing enhancement in the mechanical performance, although its durability is barely evaluated. So, this research produced eco-friendly structural concretes of three compressive strength classes and for similar application parameters. The evaluations were performed in concretes with total replacement of conventional aggregates by steel slag aggregates, containing no chemical admixtures and in the presence of a PCE-based superplasticizer. The mechanical performance and resistance to carbonation of these products were evaluated. An accelerated carbonation test was proposed and adopted to better understand the carbonation phenomenon within the research timeframe. The steel slag concretes presented higher compressive strengths and reductions in carbonation depths up to 60% compared to conventional ones. These results corroborate the technical feasibility of applying steel slag as aggregates in cement-based composites.

Performance of metakaolin/slag-based geopolymer concrete made with recycled fine and coarse aggregates

In this paper, the potential use of both fine and coarse recycled demolition aggregates (RA) in geopolymer concrete (GC) manufacturing was investigated. The geopolymer binder adopted was a mix of metakaolin (MK) and granulated blast furnace slag (GBFS), activated by an alkaline solution (SiO2/Na2O=1.8) with a water to solid ratio of 0.5. A control GC (0% RA) with C35/45 class of compressive strength and S4 class of workability, and three GC mixtures with 10, 30 and 50% of RA were manufactured. It was found that the introduction of pre-saturated RA in GC mixtures does not affect the class of workability, but the slump loss over time decreased proportionally to the RA percentage. With 10% of RA, a slight decrease was recorded in both water porosity and mechanical performances. Moreover, a drop of 18 and 27% in compressive strengths was recorded with 30 and 50% of RA incorporation, respectively. Based on the obtained results and an extensive number of experimental data from the literature, the validity of empirical relationships between the mechanical performances of GC was assessed, and more adequate predictive equations were proposed.

Cement Building Materials with Powdered Optical Discs as a Filler

The object of study is a cement composite material with powdered utilized optical discs. The objective is to establish the dependences of the main strength characteristics – com-pressive strength, bending strength, and density – on the amount of waste added into the mix-ture and the water-cement ratio.The compositions of the mixtures for the production of the cement composite material samples consisted of the following components: cement, sand, powdered waste in the form of utilized optical discs and water.Based on the results of testing the samples, mathematical models have been developed which describe the dependences of the physical and mechanical properties of the cement com-posite material samples on the fraction of waste and water-cement ratio. It was found that with an increase in the amount of powdered waste added into the mixture, it reduces the compressive strength, bending strength, and density of the samples under study, however, the optimization of the water-cement ratio makes it possible to obtain equal strength compositions with a differ-ent fraction of waste.Component compositions of cement composite material mixtures with the addition of powdered utilized optical discs in the amount of 10 to 25 % of the total filler mass, which can provide construction products with a compressive strength class B20, are presented.

PEMANFAATAN ABU LIMBAH KERTAS PADA PEMBUATAN BATU BATA

The increasing number of population each year makes the number of building needs for houses, buildings, schools, offices and other infrastructure will increase. In general, building consumption cannot be separated from the use of bricks as a form of wall construction in building construction. The size and compressive strength of bricks circulating in the market are of poor quality which comes from fabrication, local work or home industries. In the brick-making process, bricklayers only use certain types of soil to maintain the quality of brick production. As a result, the availability of soil as the main material in brick making will decrease. Another alternative to meet the shortcomings of the brick-forming material and make it stronger and more durable, can be used as a substitute for other materials such as waste paper. The use of paper waste is an effort to find new types of building materials and to reduce environmental pollution problems due to paper waste. This study aims to analyze the concentration of the addition of paper waste ash on the strength of the bricks. The benefit of this research is as an alternative study of meeting the needs of brick raw materials for environmentally friendly buildings by utilizing paper waste ash. The results showed the effect of a mixture of paper waste ash as a clay additive on the compressive strength of normal bricks (fc '2.9 MPa). The percentage value of compressive strength with a mixture of paper waste ash 3% obtained an average compressive strength of 40.10 kg / cm2, 5% mixture variation obtained an average compressive strength of 61.48 kg / cm2 and 7% mixture variation obtained an average compressive strength average 64.12 kg / cm2 against the compressive strength of normal bricks 37.28 kg / cm2. The conclusion of this research is that the variation of the mixture of paper waste ash with a variation of 7% paper waste ash mixture exceeding 60 kg / cm² (compressive strength class III) SNI 15-2094-2000a. This shows that paper waste ash can increase the compressive strength of bricks.

RSM-based optimized mix design of recycled aggregate concrete containing supplementary cementitious materials based on waste generation and global warming potential

Rapid increase in waste generation is one of the biggest environmental problems in the construction industry. Special attention has been given to using industrial wastes such as supplementary cementitious materials (SCMs) and recycled aggregates (RA) in concrete. In this research, optimizing the mix design of concrete containing recycled concrete aggregate (RCA), silica fume and ground granulated blast furnace slag (GGBFS) with different compressive strengths was performed in terms of global warming potential (GWP) and service life. In fact, the environmental impacts (GWP, waste generation and recycling potential and consuming natural resource) of plain concrete and optimal recycled concretes were compared for mixes having similar compressive strength (CS) and service life. First, an experimental investigation on the mechanical and durability properties of concrete was conducted using response surface method (RSM). Next, optimization technique was used to determine optimal mix designs with maximized service life and minimized GWP and waste generation for 6 classes of compressive strength. According to the results, comparison without considering the service life of mixes (even in equal range of CS) could lead to a significant underestimation. For instance, without considering the service life, the reduction in GWP for optimal mix designs was 41% whereas this reduction considering an equal service life was 80%. Also, compared to the plain concrete, waste generation of the optimal mix was reduced from 6412 kg to 2605 kg in a 110-year period, and 425 kg of waste per 1 m3 is recycled in this mix design.

The impact of MSWI bottom ash as aggregate on concrete mechanical performance

ABSTRACT This research investigates if bottom ash produced by incinerating municipal solid waste after recovery of metals and aging (weathering) can be used as a substitute for natural aggregates in the manufacture of concrete without additional treatment, rather than being disposed of in landfill. In this research, the performance of eight concrete mixtures that contained different amounts (0–100%) of MSWI bottom ash was analysed. Mixtures were produced by fully replacing coarse aggregate, fine aggregate, and then both of them with MSWI bottom ash and mixing with two amounts (340 and 300 kg/m3) of cement (CEM I 42.5 R). Reference mixtures were produced as well. The influence of MSWI bottom ash as aggregate on concrete performance was evaluated in terms of density, compressive strength and flexural strength. The effect of cement content was investigated as well. In addition, the changes in density and compressive strength after 2 days, 7 days and 28 days were analysed. The research showed that concrete with a compressive strength class of C20/25 and bending strength of 3.4–4.3 MPa can be produced by fully replacing coarse or fine aggregate. To achieve this, at least 340 kg/m3 of cement is required.

Influence of concrete strength, fiber content and aspect ratio in the residual flexural strength of steel fiber reinforced self-compacting concrete

Abstract Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) is a material that combines the benefits of self-compacting concrete in the fresh state and the greater durability, with the gains of fiber- reinforced concrete in the hardened state, especially the gains in residual flexural strength. Results are presented in this paper of residual flexural strengths on 48 prenotched prisms conducted in accordance with RILEM TC 162 TDF for the Steel Fiber Reinforced Self-Compacting Concretes (SFRSCC). This article presents equations to estimate residual flexural stresses in SFRSCC. For this, SFRSCC prisms of two compressive strength classes, 20 MPa and 40 MPa, were produced with 3 different types of steel fibers with the contents volume of 0.5% and 1.0%. Based on the test results, equations were proposed to determine the residual flexural stresses established through regression analysis, which were, then, further validated with concretes produced in this work and results available in the literature. The equations found, despite showing an indication of the residual flexural strengths that will be achieved, obtained a relatively high error. In order for the equations to be applied in a technical way, further studies for a larger sample need to be carried out, seeking to optimize the equations.

Freeze/Thaw Resistance Classes of Concretes

Abstract The freeze/thaw phenomenon is of interest for the field of transport infrastructure through the degradations it produces in the structure of construction elements. The climatic specificity of Romania on the one hand and the exposure to aggressive environments of construction elements in transport on the other hand, determine the importance of studying this phenomenon, its mode of action/propagation and also prevention and maintenance to ensure the functionality of buildings in transport infrastructure. Currently, in the Romanian regulations [*], the assurance of sustainability is done, as in most national annexes for the application of EN 206 [1] in Europe, by a descriptive approach (concrete “designed to last”) referring to (with mandatory status) a series of requirements of the concrete composition (water / cement ratio, minimum cement dosage, entrained air, freeze/thaw resistant aggregates, etc.) and to the compressive strength (concrete compressive strength class) in depending on the classification of the element in a certain exposure class “X”. The support of this descriptive national approach was based on the analysis of a large number of results obtained in a complex experimental program carried out by Technical University of Civil Engineering Bucharest, by analyzing the results obtained by laboratory tests on “candidate” cements and cements “reference” (having a good behavior and traditional use) as well as “in situ” tests/determinations on construction elements made with both categories of cements and maintained in specific environments. At European level, performance approaches to sustainability have made clear progress. The development of accelerated laboratory experimental methods, the establishment of performance criteria, classes of resistance to various environmental actions and the link between them and the classes of exposure to various environmental actions were the starting point for experimental research whose results will be presented in this article. Thus, in conjunction with these modern approaches, an analysis will be presented on the experimental results obtained in research on freeze/thaw resistance to different types of cements, carried out in collaboration with the laboratory of the Reinforced Concrete Structures Department, Technical University of Civil Engineering Bucharest and proposals for classification in different classes of freeze/thaw resistance.

Mixture Optimization of Recycled Aggregate Concrete Using Hybrid Machine Learning Model.

Recycled aggregate concrete (RAC) contributes to mitigating the depletion of natural aggregates, alleviating the carbon footprint of concrete construction, and averting the landfilling of colossal amounts of construction and demolition waste. However, complexities in the mixture optimization of RAC due to the variability of recycled aggregates and lack of accuracy in estimating its compressive strength require novel and sophisticated techniques. This paper aims at developing state-of-the-art machine learning models to predict the RAC compressive strength and optimize its mixture design. Results show that the developed models including Gaussian processes, deep learning, and gradient boosting regression achieved robust predictive performance, with the gradient boosting regression trees yielding highest prediction accuracy. Furthermore, a particle swarm optimization coupled with gradient boosting regression trees model was developed to optimize the mixture design of RAC for various compressive strength classes. The hybrid model achieved cost-saving RAC mixture designs with lower environmental footprint for different target compressive strength classes. The model could be further harvested to achieve sustainable concrete with optimal recycled aggregate content, least cost, and least environmental footprint.

Shear Resistance of Low Height Precast Concrete Lintels

The scope of the paper is to investigate analytically and determine experimentally the shear resistance of low height reinforced precast concrete lintels. The chosen procedures included in national and international standards applied for the design of structural concrete elements to an estimation of shear behaviour of reinforced concrete elements are described. The characteristic and designed shear strength of precast concrete lintels are determined and compared with experimentally obtained results. The shear resistance for precast concrete lintels was determined by laboratory tests according to a European standard. The assessment of the in-situ compressive strength of concrete in precast concrete lintel is specified. The designed compressive strength class is confirmed. The real reinforcement distribution is verified to assess the wide scatter of experimentally obtained failure forces. A short literature outlook of the papers concerning investigations on lintels and shear resistance of concrete is given also. The paper can provide scientists, engineers, and designers a theoretical and experimental basis in the field of precast concrete lintels shear resistance.