Properties Of Cement Systems Research Articles

SECONDARY RESOURCES IN PRODUCTION OF COMPOSITE BUILDING MATERIALS BASED ON CEMENT

Link for citation: Kopanitsa N.O., Demyanenko O.V., Kulikova A.A., Tkach E.V., Shestakov N.I., Stepina I.V. Secondary resources in production of composite building materials based on cement. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 49-60. In Rus. The relevance of the research is caused by the importance of the problem of rational use of natural resources in production of composite building materials. The possibility of partial replacement of natural non-renewable raw materials used in the production of multi-ton concrete and mortar mixtures based on cement with secondary products from the production of various industries will solve the problems of: resource saving, energy consumption and ecology. The construction industry is the largest consumer of by-products of mining enterprises: overburden and waste from mining and processing enterprises, which is hundreds of millions of tons per year. The most studied are the issues related to their use as fine and coarse aggregates in concrete and mortar mixtures for various purposes. The expansion of the possibility of using secondary products of mining enterprises in the production of composite building materials is associated with the production of active mineral additives, fillers in concrete and mortar mixtures, as well as energetically active nanomodifiers. The use of by-products of different chemical composition and dispersion makes it possible to control the processes of structure formation and hardening of composite materials based on cement and to obtain composite materials with the required performance properties. The main goal of the research is to scientifically substantiate and investigate the possibility of using waste from mining enterprises as components in concrete and mortar mixtures based on cement. Objects: modifying additives based on secondary products; composite materials with enhanced performance properties. Methods: determination of the mobility of mixtures, normal density, hardening time, flexural and compressive strength according to SS; thermal analysis; electron microscopy, x-ray phase analysis, colorimetry. Results. The paper introduces the results of studies necessary for the scientific substantiation, development and implementation in the construction industry of the technology for production of building mortar mixtures obtained using secondary products of mining enterprises as well as the comparative results of studies on the effect of a complex additive of microcalcite and nano-SiO2 on the properties of cement systems. It is shown that the introduction of a complex additive increases the compressive strength of cement stone, reduces the consumption of cement without reducing its standard characteristics and improves the performance properties of concrete.

Flowability, Strength, and Water Absorption of Mortars Containing Fly Ash and WRA Having Varying Main Chain Lengths

Within the scope of this study, the effect of the main chain length of polycarboxylate-based water-reducing admixture (WRA) on the fresh properties, compressive strength, and water absorption of mortar mixtures containing fly ash was investigated. Three WRAs with the same structure but different main chain lengths and resultantly different molecular weights were used. Effects of the admixtures on the properties of cementitious systems with 0, 15, 30, and 45 wt.% fly ash were investigated. Irrespective of the fly ash substitution level, the fluidity of the mixtures was improved when the admixture main chain length was increased up to a certain level. Possibly beyond a certain main chain length, the entanglement of too large main chains of the polymer to each other reduced the electrostatic effect of the polymer. Thus, the flow properties of the mixtures were affected negatively. The side chain molecular weight (length) of the admixtures was fixed (2,400 g/mol). However, the molecular weight of the admixtures was adjusted as 24, 48, and 71 kg/mol by changing the main chain length of the polymer. The admixture with 48 kg/mol molecular weight showed the best performance in terms of mortar fresh properties. However, the change in the length of the main chain of admixture did not have a considerable effect on the compressive strength and water absorption of the mortar. In addition, apart from the WRA admixture property, time-dependent flow and permeation properties of the mixtures were affected negatively by the increase in fly ash substitution level.

Influence of Metakaolin on the Properties of Cement Systems

Finely dispersed mineral additives containing amorphous SiO2 are successfully used in cement concretes for various purposes. Their use is due to increased durability, strength, water resistance. One of the most famous and widely used pozzolanic modifiers is microsilica. Microsilica is obtained from a waste from the production of siliconcontaining alloys containing up to 95% pure amorphous silica. Microsilica has such a disadvantage as highwater demand. To compensate, the introduction of a large amount of superplasticizer is required. In recent years, highly active metakaolin (MTK) has become increasingly popular in the world as a highly effective pozzolanic additive. This is an artificial environmentally friendly material produced from pure kaolinites. The growing popularity of MTK is due not to the fashion for new products, but to the objective advantages of this material. The purpose of this work is to study the use of metakaolin as an additive in the production of cement concrete coatings, to determine the main mechanical properties of cement beams based on activated metakaolin. Scientific research methods at work – analysis, observation, experiment, modeling

Effect of superplasticizers with different anchor groups on the properties of cementitious systems

We herein reported a series of superplasticizers that were synthesized from the macro-monomer polyethylene glycol methacrylate and the monomers acrylic acid, sodium allyl sulfonate, or vinylphosphonic acid at different molar ratios. In order to explore the influence of COO-, SO32-, and PO32- on the performance of superplasticizers, fluidity tests and plastic viscosity tests were carried out to evaluate the dispersion performance of these polymers. Furthermore, the conformation of these superplasticizers in calcium hydroxide solution was analyzed via dynamic light scattering and Ca2+ concentration tests. The results showed that these superplasticizers exhibited the best dispersion effect when the molar ratio of COO-:SO32- and COO-:PO32- was 3:1. In addition, the calcium complexing capacity of the phosphonate groups was higher than that of the sulfonate ions, leading to the lower plastic viscosity of cement pastes containing the superplasticizer with COO-:PO32- at a ratio of 3:1. This study provides valuable information for the application in practical engineering.

Effects of crosslinked polycarboxylate superplasticizers with crosslinking agent containing ester and amide groups on the properties of cementitious systems

AbstractHerein, crosslinked polycarboxylate superplasticizers were synthesized using acrylic acid, sodium methylallyl sulfonate and methyl polyethylene glycol acrylate as monomers, and monomers that contain either ester or amide groups as crosslinking agents. The superplasticizers that were synthesized from the ester‐ and amide‐based crosslinking agents were respectively denoted as SP‐E and SP‐N. In addition, a series of performance characterizations were carried out to explore the influence of different functional groups in crosslinking agents on the performance of superplasticizers. Fluidity test results showed that the dispersibility and fluidity retention of cement pastes treated with the SP‐E were better than those of cement pastes treated with SP‐N. Meanwhile, the viscosity of the sample containing SP‐E was lower than that containing SP‐N. In addition, the amount of the two superplasticizers that had become adsorbed onto the surfaces of cement particles also differed, and in this case the adsorption capacity of SP‐E was greater than that of SP‐N. X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy tests showed that the ester‐group based SP‐E superplasticizers promoted cement hydration to a greater degree than that was achieved with their amide‐bearing SP‐N counterparts. This study would provide valuable insight for the development of crosslinked polycarboxylate superplasticizers.

Effect of nonionic side chain length of polycarboxylate-ether-based high-range water-reducing admixture on properties of cementitious systems

Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures, most previous reports on the cement-admixture compatibility did not provide sufficient information on the structure of the admixture. Hence, the evaluation and generalization of the reports on the cement-admixture compatibility are challenging. In this study, three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content, anionic/nonionic molar ratio, and main chain length and different side chain lengths were produced. The compatibility of these admixtures with a CEM I 42.5 R-type cement was investigated. In addition, an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type, admixture/cement ratio, and elapsing time to the Marsh funnel flow time, mini-slump, slump flow, and compressive strength. The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems. However, the admixture having the shortest side chain was better with regard to flow retention. The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures. Regarding the behaviors of the admixtures in the cementitious systems, an optimal admixture side chain molecular weight is proposed.

Properties of cementitious systems in presence of nanomaterials

Nanomaterials have shown tremendous applications in different sectors. Nanomaterials of different size and shape when added in small amounts to cementitious systems like cement paste, mortars and concretes, there is an enormous improvements in their properties. Nanomaterials increase mechanical properties, decrease pore size and pore size distribution, modify microstructure, accelerate hydration reactions, increase durability, etc. Effects on the properties of cementitious system have been discussed. The effect of number of nanomaterials like nanosilica, nanocarbon, nanoclay and nano calcium carbonate on the properties of cementitious systems has been discussed.

IMPACT OF MULTI-WALLED CARBON NANOTUBES ON WOOD SAWDUST EXTRACT CEMENT MORTAR

It is well known that organic waste materials deteriorate the performance of concrete. The impregnation of organic aggregates and their application in combination with other chemical admixtures and mineral additives are used in order to improve the concrete properties in case of their modification by organic components. The current research is focused on the evaluation of impact of multi-walled carbon nanotubes (MWCNT) on the properties of cement systems prepared based on wood sawdust extract (WSE). The setting time, density, consistency, flexural and compressive strength, water absorption tests were undertaken. The retardation effect of (WSE) on the initial and final setting time of cement paste was observed. The additional modification of cement paste with WSE by MWCNT in the dosage of 0.005% by weight of cement (bwoc) did not show the significant changes in initial and final setting time. The application of MWCNT in the dosage of 0.005% bwoc contributed to the increase of early strength of cement mortar prepared with WSE.

COMPLEX MODIFYING ADDITIVES FOR CEMENT CONSTRUCTION MIXES

It is currently relevant to study the use of local waste based on mineral finely dispersed additives similar to substances that are formed as a result of cement hydration, which ensures high quality, increases frost resistance and forms a dense dissolved mixture. Reducing the consumption of a binder in mortar and concrete mixtures due to the introduction of modifying additives is also an important research field. The paper presents the results associated with pro-ducing a complex modifying additive consisting of waste products from marble and silicon di-oxide nanoparticles and its effect on the properties of cement systems. It is shown that the introduction of a modifying additive, while reducing cement consumption, can increase the compressive strength of cement paste up to 56 %. The X-ray phase analysis is used to determine the composition of the modified cement paste. The efficiency of using marble production wastes together with SiO2 nanoparticles as a complex modifying additive is evaluated to im-prove the properties of the cement mix.

Effect of the type of superplasticizer on the properties of cementitious systems incorporating slag

Superplasticizers have become an integral ingredient in the formulation of concretes. After 40 years, their use and dosage remain uncertain due to variations in their compositions and those of cement. In addition, the substitution of cement by supplementary cementitious materials having different chemical compositions exacerbates the problem without counting the multiplicity of superplasticizers to choose from. The present work consists of a study of the rheological and mechanical properties of cementitious systems containing slag and various types of superplasticizers. The tests were carried out on pastes, mortars and concretes incorporating slag in partial cement replacement and four superplasticizers types, polynaphthalene sulphonate (PNS) and three polycarboxylates (PC). The results of this study demonstrate that the viscosity and the yield stress increase with the rate of incorporation of the slag. The air increases with the polycarboxylates but this effect is less perceptible in the presence of the slag. Polycarboxylates improve workability more than PNS. The use of polycarboxylates reduces the viscosity and the yield stress. The compressive strength of concretes containing slag is low at early age but high at long run. They exhibit good resistances to scaling. The permeability to chloride ions is considerably reduced in the presence of the slag independently of the type of superplasticizer, suggesting good durability of these concretes in potentially aggressive external environments.

The Combined Effect of the Plasticizer and Multi-Walled Carbon Nanotubes on the Cement Hydration Products

There are many research devoted to the influence of carbon nanotubes (CNT) on the structure and properties of cement systems. In the course of this research, the combined influence of of multi-walled carbon nanotubes (MWCNT) and polycarboxylate (PCE) plasticizer on the products of hydration and the properties of hardened cement paste was investigated. The strength characteristics of nanomodified hardened cement paste and the hydration products were determined by the usage of modern methods of physico-mechanical and physico-chemical analyses. Based on the physico-chemical investigations, it was concluded the necessity of additional experiments, associated primary with questions of uniform distribution of the nanostructures and their chemical interactions with another components of admixture and cement system.

The investigation of multi-walled carbon nanotubes dispersion and its influence on rheological properties of cement systems

The current research is devoted to the studying of multi-walled carbon nanotubes (MWCNT) dispersion and its influence on the rheological properties of cement pastes. The pH and electrical conductivity test, zeta potential measurements, particle size analysis were performed for characterization of MWCNT dispersion. The MWCNT dispersion were tested during 1 month and presented the decrease of pH level from 8.89 to 8.02, increase of electrical conductivity from 2.00 to 2.75 mS/cm. The particle size analysis did not reveal the significant changes during 1 month of storage. The rheological test of nanomodified cement pastes were performed for concentration of MWCNT dispersion in the range from 0 to 0.5% by weight of cement. The decrease of yield stress by 30.7% and increase of plastic viscosity by 29.6% were obtained for cement paste modified by MWCNT dispersion in dosage of 0.25% by weight of cement. The changes in flow behaviour were established for cement pastes tested in 5 min after mixing and were not observed for cement pastes tested after 120 min of mixing.

Effect of molecular weight of slow-release Polycarboxylate Superplasticizer on the properties of cementitious system

In order to improve the fluidity retention performance of cement, monomers containing ester groups were introduced into slow-release polycarboxylate superplasticisers (PCEs). Four slow-release PCEs with different molecular weights (Mw) were synthesised through aqueous free radical polymerisation. The effect of the molecular weight of slow-release PCEs on the dispersion performance, hydrolysis reaction ratio, adsorption process and hydration of cement was investigated systematically. Due to the hydrolysis reaction, the amount of adsorbed groups continued to increase over time. The adsorption amount of PCEs on the cement particles increased with increasing Mw, indicating that Mw was the main factor affecting adsorption. The retardation of cement hydration was weakened with increased Mw, due to a reduction in the number of molecules adsorbed on the surface of the cement particles. Among the four PCEs, the PCE with medium Mw displayed excellent initial dispersion. The PCE with the highest Mw exhibited the worst dispersion retention, the strongest adsorption capacity and the most cement hydration acceleration. The PCE with the lowest Mw showed outstanding dispersion retention and the maximum delay in cement hydration. According to fluidity retention requirements, an appropriate Mw may be thus selected, which provides a reference for the synthesis and performance of slow-release PCEs.

Influence of Ultrafine 2CaO·SiO₂ Powder on Hydration Properties of Reactive Powder Concrete.

In this research, we assessed the influence of an ultrafine 2CaO·SiO2 powder on the hydration properties of a reactive powder concrete system. The ultrafine powder was manufactured through chemical combustion method. The morphology of ultrafine powder and the development of hydration products in the cement paste prepared with ultrafine powder were investigated by scanning electron microscopy (SEM), mineralogical composition were determined by X-ray diffraction, while the heat release characteristics up to the age of 3 days were investigated by calorimetry. Moreover, the properties of cementitious system in fresh and hardened state (setting time, drying shrinkage, and compressive strength) with 5% ordinary Portland cement replaced by ultrafine powder were evaluated. From SEM micrographs, the particle size of ultrafine powder was found to be up to several hundred nanometers. The hydration product started formulating at the age of 3 days due to slow reacting nature of belitic 2CaO·SiO2. The initial and final setting times were prolonged and no significant difference in drying shrinkage was observed when 5% ordinary Portland cement was replaced by ultrafine powder. Moreover, in comparison to control reactive powder concrete, the reactive powder concrete containing ultrafine powder showed improvement in compressive strength at and above 7 days of testing. Based on above, it can be concluded that the manufactured ultrafine 2CaO·SiO2 powder has the potential to improve the performance of a reactive powder cementitious system.

Effect of molecular weight of sulfanilic acid-phenol-formaldehyde condensate on the properties of cementitious system

The effect of the molecular weight of sulfanilic acid-phenol-formaldehyde condensate (SPF) on the properties of cementitious system was investigated. It is found that SPF with the molecular weight of 35,000 Dalton (Da) gives a good adsorption capacity on the surface of the cement particles, hence a larger zeta potential to cement particles and a good fluidity to the cement paste. In addition, this fraction has a high chelating capacity to calcium in the cement slurry, causing a long retardation of the cementitious system. However, the fractions of a high molecular weight (42,000 Da, and 45,000 Da) exhibit lower bleed water as a percentage of total mix water (BWP). It can be deduced that there is an ideal molecular weight for the best performances of the superplasticizer investigated, which can be used for optimizing the technical parameters in the preparation.

Characteristics of the ultrafine component of fly ash

Post-production processing of fly ash (FA) is an important issue for its use in concrete. Given (i) the need for environmental protection, (ii) the measures being applied on coal-fired power stations to reduce acidic gas emissions and (iii) the effect these have had on fly ash quality, there is a need to consider efficient post-production processing to enhance fly ash characteristics. This is particularly important for fly ash used as a cement in concrete production, since the additional residual carbon content and decreased fineness significantly affect its quality. This paper details the material characteristics of an ultrafine, low-lime fly ash (UF-FA), produced, in this case, by processing a coarse FA (referred to as parent FA) from a bituminous coal-fired power station via air-cyclonic separation. The UF-FA is shown to have much improved material characteristics compared to the parent FA in terms of morphology, mineralogy and chemical composition. Further results are presented on the effect of UF-FA on the properties of cementitious systems. Improved consistence and compressive strengths of combined Portland cement (PC) and UF-FA mortars were observed, whilst enhanced PC hydration and a high degree of FA reactivity were concluded from heat of hydration measurements and calcium hydroxide contents of pastes.

Properties of cementitious systems containing silica fume or nonreactive microfillers

The object of this work was to explore the effects of silica fume on the microstructure of hardened paste and of the transition zone between paste and aggregates in concrete. The significance of aggregates as reinforcing fillers and their impact on some properties of the transition zone and bulk paste were resolved. The experimental procedure was based on simultaneous studies of model concretes and paste matrices extracted from fresh model concrete mixes. In addition, continuously graded aggregate concretes were prepared. Three sizes of a nonreactive microfiller (carbon black) and one reactive microfiller (silica fume) were applied. On the basis of microstructural studies and compressive strength tests, it was concluded that the primary effect of silica fume was generated by its physical (microfiller) properties, since the strengthening provided by reactive silica fume was similar to that obtained with nonreactive carbon black of similar size and shape. This effect was more significant from the point of view of the concrete strength enhancement than the chemical (pozzolanic) activity of the silica fume. In concretes containing either silica fume or carbon black, aggregates of high quality could serve as reinforcing filler. This could take place when sufficient densification of the transition zone occurred in the presence of silica fume or carbon black. Significant refinement of pore structure was observed in both types of paste matrices (containing silica fume or carbon black). However, this led to a relatively small influence on the paste strength. Concretes containing reactive silica fume or an inert carbon black microfiller behaved as a composite material, unlike conventional concrete.

Rheology of Cementitious Systems

Many of the useful properties of Portland cement concrete stem from chemical reactions between cement and water, which cause the slow transformation of the initial fluid suspension into a rigid solid. Because this transformation does not begin immediately, concrete may be processed—mixed, transported, consolidated into a mold, and given a smooth surface — before it becomes rigid (i.e., sets), which typically occurs a few hours after initial mixing. As a result of the need to maintain a workable suspension during processing, the flow properties of cementitious systems have seen considerable attention. However, control of workability remains poorly understood, in part because the relationships between flow and process-ability are not clear. Recent advances have been made in understanding the flow of nonreactive suspensions, and the objective of this article is to explore how these advances provide new insights concerning the behavior of cementitious materials.There are two motivations driving investigations of cement rheology. The first is that understanding flow properties is the key to better processing. The second is that paste rheology can be used to gain a fundamental understanding of the initial cement microstructure and of the variables influencing early cement hydration reactions.