Cement-sand Mortar Research Articles

REDUCTION VIBRATIONS OF THE PILE FOUNDATIONS FOR MACHINES UNDER DYNAMIC LOADS BY HIGH-PRESSURE GROUP INJECTION METHOD

The vibration parameters of the foundations under dynamic loads or kinematic excitation directly depend on the stiffness and damping parameters of the base, the mass of the oscillating system consisting foundation, the machine and the «attached mass of soil». In the process of using pile foundations static load is transferred to the piles, the contact of the grillage with the ground is broken, and micro-gaps are formed. Micro-gaps impede the joint work of the soil mass of the inter-pile space with the foundation. An effective way to reduce the vibration parameters of foundations is the method of high-pressure group injection. The essence of the method lies in injection of a mobile cement-sand mortar into the soil base under the sole of the grillage under pressure exceeding the structural strength of the soil simultaneously through several injectors. The injection mixture eliminates micro-gaps and hardens the soil, which leads to an increase in the rigidity of the base and the involvement of an additional volume of soil mass in joint work with the foundation. The inclusion of inter-pile soil in joint work significantly increases the mass of the oscillating system and, as a result, reduces the parameters of horizontal and vertical vibrations of the pile foundation under dynamic loading and in the case of kinematic excitation. Injectors are immersed under the sole of the grillage through specially provided openings - injection conductors. The discharge points are usually located between piles and around the perimeter of the grillage. The parameters of the injection work (the number of injection points and their placement in the plan, the height of the injection horizons, the required volume of injected solution, the injection sequence, etc.) are assigned depending on the construction of the pile foundation, the engineering and geological conditions of the site, the dynamic operating mode of the equipment, and others factors. Strengthening pile foundations for machines under dynamic loads or vibration-sensitive equipment by high-pressure group injection can significantly reduce the amplitude of horizontal and vertical vibrations of foundations.

Characteristics of CFRP strengthened masonry wallettes under concentric and eccentric compression

Strengthening of masonry walls using Fibre Reinforced Polymers (FRP) sheets have shown to improve the lateral (in-plane and out-of-plane) resistance and deformation characteristics. While the improvements in shear and flexural resistances of FRP strengthened masonry are well understood, their simultaneous influence on the compression resistance of the masonry is not well explored. Therefore, this study aimed to understand the contribution of Carbon Fibre Reinforced Polymer (CFRP) strengthening on the concentric and eccentric compression strength and deformation characteristics of masonry wallettes. Two types of clay bricks were used to construct the masonry wallettes with a commonly used cement-sand mortar. In total, 36 masonry wallettes were experimentally tested under concentric and eccentric compression. The tests results are presented and discussed in terms of observed failure modes, compressive strengths and axial deformation characteristics derived. The failure of the CFRP strengthened wallettes were mainly attributed by crushing failure of masonry. The transverse stain readings of CFRP sheets on the wallettes confirm that the composite action exists in the CFRP strengthened masonry wallettes. Further, CFRP strengthened wallettes tested under concentric compression have shown to improve the compression resistance only about 10–20 %. The stiffness and ductility of the wallettes strengthened with CFRP has improved (20–30 %) compared to the un-strengthened wallettes. Therefore it can be said that, although the CFRP application can improve the shear and flexural resistances, it does not significantly enhance the compressive strength and ductility, as the compression failure was governed by masonry crushing.

Seismic Capacity Assessment of Unreinforced Brick Masonry Building Performed According To Eurocode

Brick Masonry Building with cement sand mortar is a common type of building typology in Nepal. Regardless of being one of the eldest construction technology, the behavior of masonry building is still a matter of study. The uncertainty in the behavior of masonry structures is due to material heterogeneity, complex behavior under different loading conditions and may be due to less research in this arena. Different modeling strategies are used and proposed worldwide to design and to identify the seismic performance of Masonry Building. The analysis strategy ranges from the simple linear method, equivalent frame method, static nonlinear method to dynamic nonlinear, which may be chosen according to engineering design aims and research purpose. In this attempt, authors choose two degrees of freedom 3D model of Unreinforced Brick Masonry Structures which catches both overturning and hysteresis mechanisms due to the shear response implemented by the TREMURI program with static nonlinear procedures. This verified method of modeling and analysis is applied to assess the performance of three different Unreinforced Brick Masonry buildings of the same plans with different numbers of storey.

Сement Mortars with Alkali-Free Accelerators under Test Conditions for Alkali-Silica Reactions

The results of long-term and accelerated tests of cement–sand mortars with a reactive aggregate and additives Al2(SO4)3 and Fe2(SO4)3, carried out under the conditions of the corresponding standardized techniques, indicate that these additives suppress the development of destructive expansion deformations of mortars and concretes caused by alkali-silica reaction. In all samples of cement–sand mortars, after accelerated and long-term tests, destructive changes occurring with particles of reactive aggregate were noted. Ettringite was found in samples after long-term tests (its content is higher in samples with additives of aluminum and iron sulfates), whereas in samples subjected to accelerated tests in NaOH solution, ettringite rapidly decomposes with the formation of a hydrogarnet phase. The results of an energy dispersive microanalysis of an alkali-silicate hydrogel formed as a result of an alkali-silica reaction do not allow explaining the ability of aluminum and iron sulfates to suppress expansion deformations by their influence on the chemical composition of the hydrogel and, accordingly, on its destructive properties. It can be assumed that the presence in the samples of other phases (ettringite and hydrogarnet phase), the formation of which is promoted by additives, can have a restraining effect on the dynamics of the development of destructive expansion deformations.

Characteristics of CO2 and Energy-Saving Concrete with Porous Feldspar.

In this study, to reduce the use of cement and sand, porous feldspar with excellent economic efficiency was used as a substitute in the heat storage concrete layer. When porous feldspar and four other silicate minerals were used as substitute materials for sand in cement mortar, the specimen with the porous feldspar exhibited approximately 16–63% higher compressive strength, thereby exhibiting a higher reactivity with cement compared to the other minerals. To compensate for the reduction in strength owing to the decreased cement content, mechanical and chemical activation methods were employed. When the specific surface area of porous feldspar was increased, the unit weight was reduced by approximately 30% and the compressive strength was increased by up to 90%. In addition, the results of the thermal diffusion test confirmed that thermal diffusion increased owing to a reduction in the unit weight; the heat storage characteristics improved owing to the better porosity of feldspar. When chemical activation was performed after reducing the cement content by 5% and replacing the sand with porous feldspar, the compressive strength was found to be approximately twice that of an ordinary cement mortar. In a large-scale model experiment, the heat storage layer containing the porous feldspar exhibited better heat conduction and heat storage characteristics than the heat storage layer composed of ordinary cement mortar. Additionally, energy savings of 57% were observed.

Performance evaluation and microstructure characterization of seawater and coral/sea sand alkali-activated mortars

To adequately develop the application of marine resources for island construction and effectively promote the sustainability of industrial resources, this paper investigates the feasibility of using seawater and coral or sea sand as replacements for freshwater and river sand in alkali-activated mortars (AAMs) containing ground blast furnace slag (GBFS), fly ash (FA), and silica fume (SF). Five different mortar mixtures were designed: seawater and coral sand alkali-activated mortar (SC-AAM), seawater and sea sand alkali-activated mortar (SS-AAM), freshwater and river sand alkali-activated mortar (FR-AAM), seawater and coral sand cement mortar (SC-OPC), and freshwater and river sand cement mortar (FR-OPC). The differences in the workability (slump), setting time, compressive strength, flexural strength, and drying shrinkage of the prepared cement mortars and AAMs were compared. Then, the microstructure and crystalline phases of the mortar samples were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The experimental results indicated that the utilization of seawater and coral or sea sand promoted the formation of C-S-H gel phases. Additionally, the existence of coral sand decreased the slump and initial setting time of the mortars due to the high water absorption and porosity of the coral aggregate. The SC-AAM exhibited higher compressive and flexural strengths at an early age and had a lower drying shrinkage than other AAMs, which can be attributed to the natural internal curing effect of the coral sand and the dense interfacial transition zone between the aggregate and the binders. The weak strength of coral sand had no effect on the strength development of the mortars in AAM production. However, the SS-AAM had a relatively low compressive strength and a large drying shrinkage in comparison to other mortar samples due to the existence of more free water.

An Investigation into the Thermo-Physical, Mechanical, and Microstructural Properties of Cement Mortar Incorporating Hybrid Waste Slags

This study investigates the mechanical and thermal properties of cement mortars incorporating two types of waste slags: ferrochrome (FeCr) slag aggregate was used as a replacement for sand at ratios of 25, 50, 75 and 100 wt%, and ground granulated blast furnace slag (GGBS) was used as a partial replacement for cement at a ratio of 25 wt%. Compressive strength, volume of permeable voids (VPV), drying shrinkage, and thermal conductivity tests were conducted after 28 days of curing. The microstructure characteristics were examined by scanning electron microscopy. The experimental results revealed that FeCr waste aggregates could satisfactorily replace natural fine sand in cement mortars up to 25 wt% without a remarkable degradation of compressive strength. Furthermore, increasing the replacement ratios of FeCr aggregates by over 25 wt% resulted in a noticeable decrease in thermal conductivity and an increase in the permeable void content of cement mortars. The increased VPV of FeCr slag-blended mortars led to a significant increase in drying shrinkage. The integration of GGBS with FeCr aggregates led to enhanced compressive strength and reduced VPV and drying shrinkage, thus contributing to an improved microstructure.

Concrete Recycling as a Source of Polyfractional Mineral Raw Materials

The problems of concrete recycling as a complex poly-reinforced composite characterized by unstable composition and properties are discussed. The peculiarity of recycling concrete scrap is that its return to the production cycle can be carried out in the form of different products: coarse aggregate (recycled aggregate), fine aggregate (sand from crushed concrete), as well as in the form of a dust-like fraction. It is shown that aggregates made of crushed concrete are inferior to natural analogues due to the presence of cement-sand mortar in their composition. Given the growing threat of depletion of natural resources, it seems appropriate to consider construction waste not only as secondary resources for the production of concrete and mortars, but also more widely: as a promising technogenic source of polymineral raw materials, including for firing technologies.

Energy-efficient double-row masonry of the exterior walls in the buildings made of cellular concrete blocks

Ensuring the increased requirements for heat saving, environmental safety and comfort of residential and public buildings is one of the main directions of scientific and technological progress in construction. In particular, the cellular concrete products’ use in building envelopes is aimed at solving these problems. Cellular concrete blocks perform the wall-forming material functions and insulation simultaneously due to their thermophysical and strength characteristics. However, the factor reducing the energy efficiency of aerated concrete masonry is the filling of masonry joints with adhesive or cement-sand mortar, which are the thermometer bridges, and the use of polyurethane adhesive, which has lower thermal conductivity compared to adhesive mixtures, as an aggregate of vertical and horizontal joints is unacceptable due to its high deformability and low shear stiffness. The authors examined the systems of building envelopes made of cellular concrete blocks used in civil engineering, and identified their shortcomings that affect the energy efficiency of the entire building. The authors have developed an energy-efficient two-row masonry of cellular concrete blocks, the device of which allows to reduce the masonry thickness and facilitate the installation of the enclosing structure with equal masonry thermal conductivity.

Адсорбционные характеристики материалов ограждающих конструкций

Знание численных значений адсорбционных харак­теристик материалов ограждающих конструкций зданий необходимо для проведения расчётов теплотехнических показателей этих конструкций. Адсорбционными характери­стиками материала являются: константа с уравнения Брунау- эра-Эммета-Тейлора (БЭТ) сорбции паров воды, равновесная сорбционная влажность wm материала, соответствующая за­полнению первого монослоя адсорбированных молекул воды (ёмкость монослоя), относительной влажности воздуха фт , соответствующей заполнению первого монослоя, и удельная поверхности А материала. Существует два метода обработки изотерм сорбции паров воды исследуемым материалом с це­лью определения этих характеристик. Первый метод основан на использовании уравнения БЭТ. Второй метод, названный Ж-метод, представляет собой модификацию первого.
 Уравнение БЭТ применимо для анализа изотермы сорб­ции только в диапазоне относительных давлений адсорбата от 0,05 до 0,35. N-метод применим для анализа изотермы сорбции в диапазоне относительных влажности воздуха от 0,05 до 0,5. Таким образом, основное преимущество N-метода по сравнению с методом, основанным на уравнении БЭТ, заключается в том, что N-метод позволяет получить более точную информацию об адсорбционных характеристиках исследуемого материала, так как эту информацию получают путём обработки большего числа экспериментально полу­ченных значений равновесной сорбционной влажности этого материала.
 С целью сопоставления двух вышеупомянутых методов по этим методам были обработаны полученные на вакуумной сорбционной установке при температуре +20 °С изотермы сорбции восьми строительных материалов: цементного камня, тяжёлого бетона, керамзитобетона, азеритобетона, красного кирпича, цементно-песчаного раствора и пенобетона. По ре­зультатам обработки были определены адсорбционные харак­теристики и получены уравнения начальных участков изотерм сорбции исследованных материалов при температуре +20 °С.

Influence of the technological properties of cement-sand mortar on the quality of 3D printed products

The results of the influence of cement-sand mortar mobility on quality of hardened composites, made by 3D concrete printing (3DCP), are presented. Four formulations of cement-sand mortar mixes with mobility classes Pk 1, Pk 2, Pk 3, Pk 4 which corresponds to immersion depth of the reference cone of 3.3 cm, 6.5 cm, 8.7 cm, 12.0 cm, respectively, were prepared for testing. It has been established that regulatory framework regulating 3DCP test methods not sufficiently developed and requires further improvement. It was revealed 3D printing of cement-sand mortar mixes with mobility classes Pk 2-Pk 4 on researched 3D printer is possible, however, products have defects and damages. Mortar mobility has a significant impact on structure kinetics and geometric parameters deviation. The lower mobility class is, the higher structure kinetics of raw material mix is, which is due to the early formation of the crystallization structure of hardened composite. Cement-sand mortar with class mobility Pk 2 accepted for further research in the development of adapted raw mixes for 3DCP.

КОМПОЗИЦИОННЫЕ ВЯЖУЩИЕ ДЛЯ ОТДЕЛОЧНЫХ СОСТАВОВ

Belgorod region is one of the leading regions in housing construction, especially private households. This is due to the high demand for finishing materials, in particular, dry plaster and putty mixtures, produced mainly on the basis of gypsum. However, local producers of such products can hardly compete with imported products due to lower prices. The reason for this is the absence in Belgorod Region, as in many other regions of Russia, of gypsum deposits and, as a result, its rather high cost exceeds that of Portland cement. Such a situation makes the actual development of cement-based finishing mixtures, corresponding to gypsum consumer qualities. The main problems of obtaining plaster compositions based on Portland cement is its excessive activity, low water-holding capacity and, as a result, poor workability and adhesion to the base. The classic solution to this problem is the introduction of a fine component (clay or lime) into such a solution, which makes the solution suitable for plastering, but does not allow Portland cement to realize its strength potential, therefore, does not ensure the effectiveness of its use. Giving the cement-sand mortar the desired properties due to polymer modifiers (structuring and thickening) is unjustified due to their high cost and high consumption. In this regard, at this stage of research, the task was to obtain a mineral system based on Portland cement with properties maximally adapted to obtain plaster mixtures, in order to further produce its modification with the above-mentioned additives at their minimum consumption. Composite binders consisting of a clinker part and a mineral additive were chosen as a tool for solving the problem posed. Due to the choice of the ratio of components, their type and dispersion, processing modes, it is possible to vary the properties of the products obtained within considerable limits.

INFLUENCE OF A ACRYLAMIDE COPOLYMER ON THE PROPERTIES OF CONSTRUCTION CEMENT MORTAR

The influence of a water-soluble polymer additive based on a copolymer of acrylamide, N,N-dimet-hylaminopropylmethacrylamide and itaconic acid on the workability, colmatization and hydrophilic-hydrophobic properties of sand-cement mortar and cement stone is considered. The dosage of the polymer additive is proposed and its effect on the technological properties of the mortar mixture is evaluated: mobility, density, delamination.

Brickwork Chemical Corrosion Features

The use of multilayer enclosing structures in modern construction poses a new task of studying the mutual influence of all materials of multilayer structures on the durability of the structure as a whole. Masonry is the oldest and most representative multi-component envelopes. This work is devoted to the study of the processes of chemical destruction, taking into account the mutual influence of building ceramics (clay bricks) and cement-sand mortar. The article deals with the main process of destruction of materials, based on the destruction of the amorphous part of the brick under the influence of calcium hydroxide, penetrating into the brick of cement-sand mortar, where it is produced in the process of dehydration of calcium silicates and aluminosilicates (leaching reaction). We consider the side processes of the first type, taking into account the presence in the amorphous phase of brick oxides of alkali and alkali-earth metals.

Investigation on early-age hydration, mechanical properties and microstructure of seawater sea sand cement mortar

Using seawater for concrete manufacturing promisingly provides significant economical and environmental benefits. In this study, ordinary Portland cement (OPC) hydration in distilled water and seawater and the corresponding evolution of solid phases was investigated by heat evolution, hydrated phase, hydration kinetics, and microstructure characterization. The results show that seawater can promote the early hydration of tricalcium silicate (C3S) during the hydration acceleration period. The hydrated phase assemblage was affected by the dissolved ions in seawater. Friedel’s salt was detected as a specific hydration phase in seawater, which was formed by chemical combination between the aluminate ferrite monosulfate (AFm) phase and chloride ions. The monocarboaluminate can be converted into a stable phase as Friedel’s salt in the seawater, due to the reaction with chloride ions. Furthermore, the ettringite becomes more stable when coexists with Friedel’s salt than that with monocarboaluminate, and thus ettringite formed in seawater remains 67% higher than that formed in distilled water at the later curing age. Moreover, additional unhydrated cement and less amorphous calcium silicate hydrate (C-S-H) were formed in seawater, which might be responsible for the slightly lower compressive strength of cement mortar prepared by seawater and sea sand. A modeled evolution of the solid phase and pore solution have been established, which agrees well with the characteristics of the dissolution of mineral phase, precipitation of hydration products and changes of pore solution. The related results can provide an insight into the applications of seawater and sea sand concrete for marine infrastructures.

Sustainable mortar mix using recycled fines obtained from construction and demolition waste

Rivers are over exploited for natural sand extraction and production of cement has triggered global warming. For sustainable development a study has been conducted to use construction and demolition waste (CD-W) in cement-sand mortar. In the present study, crushed CD-W in the form of recycled concrete fine aggregate (RCFA) and recycled concrete powder (RCP) has been planned to be used in cement-sand mortar as replacement of natural standard sand (NSS) and cement, respectively. The effects of partial replacement of NSS and cement with RCFA and RCP on compressive strength and split tensile strength after 7th and 28th day of curing have been evaluated. Outcomes of elevating replacements of cement and sand in mortar have been found to be decreasing gradually, but falls above the minimum limit of 7.5 N/mm2 as established by IS: 2250 (1981) for use of mortar in structural applications. Therefore, the study concludes the valid potential of RCFA to be utilized up to 100% percent and RCP up to 20% as partial replacement of natural sand and cement, respectively in mortar production.

Evaluation of mechanical behaviour of the rubberized PCC mortar in fixed W/C ratio

Addition of the waste tire rubber powder to the cement-based products is a solution for the waste problems and protecting environment. Cement-sand mortar is an integral part of masonry buildings and has an important effect on the integrity of the masonry walls. In the current research, mechanical properties and microstructures of the rubberized mortar have been investigated over various lifetimes and the cement content of the mortar was optimized by Pareto solutions. Portland composite cement (PCC) was used for making the rubberized mortar. The amount of rubber additive to the mortar specimens is considered to be 5%. The cement and water content were the variable parameters in the mixture designs while the ratio of W/C was fixed and equalled to 0.6. The microstructure analysis of the test specimens showed that the adherence of the rubber powder particles in the mortar mixture would be more effective with increasing of the cement content, and the negative effects of using rubber powder on the mortar structure can be minimized by choosing the appropriate mixture design. Also, it shows that by increasing the amount of cement in the mixture design of rubberized mortar, the compressive, tensile and flexural strengths of the mortar would be very close to the plain mortar specimens, and in some cases, the tensile and flexural strength of the mortar specimens would be increased regarding the plain mortar specimens.

Improving Earthquake Resistance of Structures by Injection Consolidation of Earth Foundations

Based on the analysis of the results of field experiments, recommendations were developed on increasing the earthquake resistance of soil foundations of buildings and structures at the Krasnobrodsky coal open-pit mine, providing conditions for an uninterrupted and safe technological process of minerals extraction and transportation. As a result of research carried out at a pilot test site by the method of seismic sounding using the refraction technique, scientific and practical results were obtained. It has been experimentally proved that compacting soils with cement-sand mortar allows us to improve their deformation properties, which leads to an increase in the earthquake resistance of structures. The seismicity of the soil foundation of the enrichment complex of inclined separation was calculated on the basis of the performed simulation of deformation processes in the consolidated foundation of the structure in a critical state. The studies have found out that when weakened soils are compacted under the supports of the galleries of the structure and after the artificial foundation has gained strength, seismicity decreased from 7 to 6 points.

БИОМОДИФИЦИРОВАНИЕ СТРОИТЕЛЬНЫХ МАТЕРИАЛОВ БАКТЕРИЯМИ С УРЕАЗНОЙ АКТИВНОСТЬЮ

This article uses research results that allow you to get self-healing building materials based on mineral binders. This happens by adding microcontainers to dissolved mixtures, which use nutrients for bacteria with urease activity, which produce calcium carbonate, which fills microdefects in the material. The research results include the use of active forming bacteria, as well as their effect on various properties of modified mortars. To obtain soluble mixtures with different pH values, Portland cement and gypsum binder were used. Indicators of their active work. In this work, the dependence of the aquatic environment on the concentration of biomass in the dissolved building mixture, the dependence on the aquatic environment and microorganisms is shown. The results are associated with the presence of biological surfactants in bacterial cells, which have a significant effect on the rheological properties of cement-sand mortars. A change in the setting time and strength characteristics of cement-sand mortars at various cell concentrations

Contrastive Analysis on Mechanical Properties of M Sand and River Sand Cement Mortar Bricks With Partial Restoration of Rice Husk Ash

Normally Rice Husk Ash (RHA) is treated as agricultural waste that do not afford any human feed products across the globe, these kind of agricultural waste can be converted into a convenient product and also M sand is used as a substitute for the river sand, the proportions of river sand from 100%, 75%, 50%, 25%, 0% were restored by M sand, along with that rice husk ash in various proportions from 0%, 5%, 10%, 15%, 20%, 25%, 30% to determine the optimum percentage of rice husk ash without affecting strength properties of bricks. The optimum restoration of 35% of RHA delivered the average compressive strength of 5.34 MPa which is higher than that of common buildingbricks.