Cement Mass Research Articles

Study on the damage resistance and deterioration behavior of GO concrete under the harsh environment.

To exploretheeffects of physical, mechanical, anti-deterioration properties of graphene oxide (GO) on cement-based cementitious materials, GO sheet dispersions areprepared by the improved Hummers method and ultrasonic dispersion method. The influence of theGO content on the compressive and flexural strengths of cement paste is investigated, and the penetration process of chloride ions in graphene oxide concrete is discussed by the electric accelerated erosion method. Combined with the rapid freeze-thaw test, the deterioration of graphene oxide concrete ismethodically analyzed. Theobtained results reveal that an appropriate amount of GO improves both the compressive and flexural strengths of cement pastev. In the chloride environment, the chloride diffusion coefficient of 0.03% GO concrete is 18.75% less than that of ordinary concrete.Under the action of freeze-thaw cycles, with the increase of salt freezing times, the deterioration mode of GO concrete is a combination of mortar shedding, micro-crack expansion, denudation, and block shedding; The stress-strain curve of the specimen tends to be flat with the growth of salt freezing times. The peak stress gradually lessens, the peak strain gradually grows, and the elastic modulus remarkably reduces. Compared with ordinary cement paste, theGO is capable of promoting the growth of cement paste hydration crystals, changing the size and shape of crystals, and realizingthe regulation of cement paste microstructure. Incorporating an appropriate amount of theGO could promote the cement hydration process and enhance the chemical water-binding amount in the cement paste. The optimal GO content is reported to be 0.03% of the cement mass.

The Effect of Mechanical Activation of Fly Ash on Cement-Based Materials Hydration and Hardened State Properties.

Fly ash from coal represents the foremost waste product of fossil fuel combustion. These waste materials are most widely utilised in the cement and concrete industries, but the extent of their use is insufficient. This study investigated the physical, mineralogical, and morphological characteristics of non-treated and mechanically activated fly ash. The possibility of enhancing the hydration rate of the fresh cement paste by replacing part of the cement with non-treated and mechanically activated fly ash, and the hardened cement paste's structure and early compressive strength performance, were evaluated. At the first stage of the study, up to 20% mass of cement was replaced by untreated and mechanically activated fly ash to understand the impact of the mechanical activation on the hydration course; rheological properties, such as spread and setting time; hydration products; mechanical properties; and microstructure of fresh and hardened cement paste. The results show that a higher amount of untreated fly ash significantly prolongs the cement hydration process, decreases hydration temperature, deteriorates the structure and decreases compressive strength. Mechanical activation caused the breakdown of large porous aggregates in fly ash, enhancing the physical properties and reactivity of fly ash particles. Due to increased fineness and pozzolanic activity by up to 15%, mechanically activated fly ash shortens the time of maximum exothermic temperature and increases this temperature by up to 16%. Due to nanosized particles and higher pozzolanic activity, mechanically activated fly ash facilitates a denser structure, improves the contact zone between the cement matrix, and increases compressive strength up to 30%.

Improving the Physical and Mechanical Characteristics of Modified Aerated Concrete by Reinforcing with Plant Fibers

An urgent and promising direction in the development of building materials science is the improvement of the quality of non-autoclaved aerated concrete. In view of the obvious disadvantages of non-autoclaved aerated concrete compared to the autoclaved equivalent in terms of technology, it can be significantly improved because of a rationally selected composition and other factors of a recipe-technological nature. The goal of the study was to search for complex compositions and technological solutions aimed at identifying rational combinations of recipe-technological factors as simultaneous modifications of aerated concrete with various additives and dispersed the reinforcement of it with various environmentally friendly and cost-effective types of plant fibers. Fly ash (FA), instead of part of the cement, proved to be more effective than the GGBS additive. The compressive strength (CS), bending strength (BS), and coefficient of construction quality (CCQ) were higher by 4.5%, 3.8%, and 1.7%, respectively, while the density and thermal conductivity (TC) were lower by 0.7% and 3.6%, respectively, compared with aerated concrete modified with ground granulated blast-furnace slag (GGBS). The additional reinforcement of modified aerated concrete with coconut fiber (CF) and sisal fiber (SF) in an amount of 0.6% of the total mass of cement and modifier increases the CS to 15%, BS to 22% and CCQ to 16%. The SF was more effective than the CF. Aerated concrete modified with FA and reinforced with SF showed the highest efficiency. Compared to the control composition without modifiers or fibers, the increase in the CS was up to 40%, BS up to 47%, and CCQ up to 43%, while the decrease in density was up to 2.6%, and TC up to 15%.

Effect of Nano-CaCO3 on Early-Age Properties and Cracking Potential of High-Strength Concrete

The development of nanotechnology has facilitated the application of various nanomaterials in concrete over the past decade. Few investigations have characterized early-age properties and cracking potential of concrete with nanomaterials. The present study aimed to expand the limitation by means of an experiment campaign, including a mechanical properties test, free shrinkage measurement, and restrained ring test on high-strength concrete (HSC) with nano-CaCO3 (NC). The proportions of NC were 0%, 1%, 2%, and 3% by the mass of cement. The results showed that HSC demonstrated higher mechanical properties with 1% NC incorporated. Adding NC reduced the free and restrained shrinkage of HSC. Stress relaxation and tensile creep were evaluated in this paper. The established relationship between relaxation and creep coefficients was sensibly independent of NC proportions, which contributed to better estimating the stress level in HSC with NC, so as to better evaluate the cracking potential at early age.

Research on Influences of Ultrasonic Vibration Agitation Stirring on Carbonation Resistance of Cement-Based Materials after Absorption of CO2

To disclose influences of ultrasonic vibration agitation on the carbonation resistance of cement-based materials after absorption of CO2, the variation laws in internal carbonization zone were explored by the testing carbonization depth and carbonization range (pH variation range) of cement mortar after CO2 absorption at different ages. Results demonstrated that when CO2 absorption volumes of the cement mortar before carbonization were 0.44%, 0.88%, 1.32%, 1.76%, and 2.20% (28 d), the carbonization depth under ultrasonic vibration decreased by 5.5%, 12.3%, 21.7%, 20.7%, and 26.7% compared to those under mechanical stirring, respectively. When the ultimate CO2 absorption volume increased to 2.2% of cement mass, the extended degree of cement mortar was 103.23 mm, which decreased by 5.4% compared to that before CO2 absorption. pH variation values of the carbonization range under ultrasonic vibration presented a rising trend with the increase of CO2 absorption volume of cement mortar before carbonation. This indicated that, with the increase of CO2 absorption volume of cement mortar before carbonation increases under ultrasonic vibration, the carbonization process of the hardened body of cement mortar might be decelerated to some extent. Additionally, changes in internal composition and physical images of cement-based materials after absorption of CO2 were analyzed through microtest means like SEM and XRD. A carbonation resistance model was constructed, thus enabling disclosure of the variation mechanism of carbonation resistance of cement-based materials after absorption of CO2 under mechanical stirring and ultrasonic vibration. Results demonstrated that the higher CO2 absorption volume of fresh slurry generated more “nano-level” CaCO3 crystal nucleus. Accordingly, it could improve the porous structure of the cement mortar, decrease the quantity of capillary tubes significantly, improve the compaction degree of cement-based materials effectively, and lower the diffusion rate of CO2 in the cement paste base, thus improving the carbonation resistance. Research conclusions have important significance to decrease CO2 emissions and improve carbonation resistance of concrete.

Utilization of carbonated calcium phosphate cement for contouring cranioplasty in patients with syndromic craniosynostosis.

Carbonated calcium phosphate (CCP) cement is an alloplastic material which has been increasingly utilized for cranioplasty reconstruction; however, there is a paucity of data investigating its use in patients with syndromic craniosynostosis. The purpose of this study was to characterize our institutional experience with CCP cement for secondary contouring cranioplasty in these patients to establish safety and aesthetic efficacy. Patients with syndromic craniosynostosis undergoing cranioplasty with CCP cement from 2009 to 2022 were retrospectively reviewed for prior medical and surgical history, cranioplasty size, cement usage, and postoperative complications. Aesthetic ratings of the forehead region were quantified using the Whitaker scoring system at three timepoints: preoperative (T1), < 6months postoperative (T2), and > 1year postoperative (T3). Twenty-one patients were included. Age at surgery was 16.2 ± 2.8years, forehead cranioplasty area was 135 ± 112 cm2, and mass of cement was 17.2 ± 7.8g. Patients were followed for 3.0 ± 3.1years. Whitaker scores decreased from 1.9 ± 0.4 at T1 to 1.4 ± 0.5 at T2 (p = 0.005). Whitaker scores at T2 and T3 were not significantly different (p = 0.720). Two infectious complications (9.5%) were noted, one at 4.5months postoperatively and the other at 23months, both requiring operative removal of CCP cement. Our results suggest that aesthetic forehead ratings improve after CCP contouring cranioplasty and that the improvement is sustained in medium-term follow-up. Complications were uncommon, suggesting that CCP is relatively safe though longer-term follow-up is needed before reaching definitive conclusions.

Sustainable utilization of copper post-flotation waste in cement composites

The current way of managing the copper ore flotation waste is by placing it in waste neutralization facilities. However, flotation waste has great potential in application in cement composites. The article presents the detailed characteristics of post-flotation waste (PFW) and three types of cements: CEM I, CEM II/B-V, and CEM III/A, 42.5 MPa class. The post-flotation waste added for 20% of the cement mass increase the water demand to obtain the standard consistency. The highest pozzolanic activity was noted for mortars made of Ordinary Portland Cement and cured at 20 °C. The lower curing temperature, i.e. 10 °C, delays the hydration reaction, extends setting time, and reduces compressive strength. The conducted tests showed that the specimens produced from CEM I and PFW have the highest compressive strength (after 28 and 90 days), which means that PFW does not react with silica fly ash (from CEM II/B-V) and granulated blast furnace slag (from CEM III/A). The reaction of the waste with the components of the Portland clinker is preferred. The performed studies proved that the utilization of copper post-flotation waste allows for the development of sustainable and durable composite made of CEM I and indicated the possibilities of further testing of waste, in the direction of its use as a mineral additive for concrete.

Flow Characteristics of Slurry Infiltrated Fibrous Concrete (SIFCON) with Silica Fume and Steel Fibers

SIFCON is one of the newly established buildings substantial. The proportion of silica fume additional was 17.5% through mass of cement in slurry infiltrated fibrous concrete &amp; four various bulk segments of plain mild steel fibres, crimped mild steel fibres and hooked ended mild steel fibers (0, 5, 15, 25 and 35) % were utilized. The examined belongings of fresh slurry infiltrated fibrous concrete were normal slump cone test, reversed slump cone test, mini slump cone trial, J- fibres penetration test and L-box test test which were agreed out on usual magnitude of slump cones, J-box and L-box respectively at fresh state of SIFCON slurry (mortar). The spread flow diameter for standard slump cone, inverted slump cone and mini slump cone values up to 670mm, 650mm and 175mm respectively were obtained at fresh state of SIFCON slurry (mortar).

Effect of a New Multi-Walled CNT (MWCNT) Type on the Strength and Elastic Properties of Cement-Based Mortar

Creating new construction materials with improved strength, elasticity, and durability properties represent the focus of many research works. Significant research effort has been invested in investigating the use of carbon nanotubes (CNTs) in cementitious materials, especially multi-walled carbon nanotubes (MWCNTs) which consist of a series of concentric graphite tubes. The use of MWCNTs is closely related to the use of surfactants and ultra-sonication procedures which may alter their properties and the properties of cement-based materials. The paper presents the preliminary results of an experimental investigation on the suitability of using a new, modified, MWCNT type aimed at eliminating the need of using surfactants and ultrasonication. The modified MWCNTs have a much lower surface energy compared to “classical” ones which would result in a decreased tendency of self-aggregation. A comparison was carried out from the point of view of density, flexural and compressive strength as well as dynamic modulus of elasticity of the obtained mortars. The mortar mix incorporating the modified MWCNTs showed improved mechanical properties even for a low percentage of CNT addition (0.025% by mass of cement). The results are discussed based on the material structure determined from a series of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses.

Smart Cementitious Sensors with Nano-, Micro-, and Hybrid-Modified Reinforcement: Mechanical and Electrical Properties.

The current paper presents the results of an experimental study of carbon nano-, micro-, and hybrid-modified cementitious mortar to evaluate mechanical performance, energy absorption, electrical conductivity, and piezoresistive sensibility. Three amounts of single-walled carbon nanotubes (SWCNTs), namely 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, and 0.3 wt.% of the cement mass, were used to prepare nano-modified cement-based specimens. In the microscale modification, 0.05 wt.%, 0.5 wt.%, 1.0 wt.% carbon fibers (CFs) were incorporated in the matrix. The hybrid-modified cementitious specimens were enhanced by adding optimized amounts of CFs and SWCNTs. The smartness of modified mortars, indicated by their piezoresistive behavior, was investigated by measuring the changes in electrical resistivity. The effective parameters that enhance the composites' mechanical and electrical performance are the different concentrations of reinforcement and the synergistic effect between the types of reinforcement used in the hybrid structure. Results reveal that all the strengthening types improved flexural strength, toughness, and electrical conductivity by about an order of magnitude compared to the reference specimens. Specifically, the hybrid-modified mortars presented a marginal reduction of 1.5% in compressive strength and an increase in flexural strength of 21%. The hybrid-modified mortar absorbed the most energy, 1509%, 921%, and 544% more than the reference mortar, nano-modified mortar, and micro-modified mortar, respectively. The change rate of impedance, capacitance, and resistivity in piezoresistive 28-day hybrid mortars improved the tree ratios by 289%, 324%, and 576%, respectively, for nano-modified mortars and by 64%, 93%, and 234%, respectively, for micro-modified mortars.

A Preliminary Study on the Morphological Changes of an NiTi-Shaped Memory Alloy Stent in the Vertebral Body.

At present, the most commonly used filler polymethyl methacrylate (PMMA) has the disadvantages of monomer toxicity, heat and leakage, and cannot be applied in young people. Therefore, finding a minimally invasive and good tissue-compatible alternative material has been a research hotspot in spine surgery in recent years. The aim of this study is to explore whether the memory alloy stent can avoid the complications of bone cement or not. Four non-adjacent vertebral bodies of the thoracic and lumbar spine in the 18 10-month-old pigs were selected as the surgical site and were randomly divided into the scaffold group and the bone cement group. The memory alloy scaffold and PMMA (polymethyl methacrylate) bone cement were placed via percutaneous puncture, and intraoperative fluoroscopy and micro-CT were used to observe the changes in the height of scaffolds and bone cement in the vertebral body immediately, 6 weeks, and 12 weeks after operation, the microstructural parameters of the bone trabeculae (bone volume fraction, bone surface volume ratio, bone trabeculae number) were also measured. The memory alloy stent could expand in the vertebral body, and its height gradually increased with time; additionally, the height of the bone cement mass did not change with time (p=0.00). New bone trabeculae could grow into the scaffold along the gap, and the volume fraction of bone, the volume ratio of bone surface area, and the number of bone trabeculae increased gradually (p=0.00). However, the volume fraction of bone, the volume ratio of bone surface area, and the number of trabeculae in the cement block decreased gradually (p=0.00). Memory alloy scaffolds have dynamic expansion characteristics in vivo, which can effectively avoid the complications of bone cement. Thus, it is beneficial to explore this minimally invasive treatment for vertebral compression fractures.

Using volcanic pumice dust to produce high-strength self-curing concrete in hot weather regions

The aim of this research is to investigate the influence of cement mass replacement with volcanic pumice dust (VPD) at levels of 10 %, 20 %, and 30 % on the performance of high-strength concrete (HSC) under submerging (SuC) and internal curing (InC) methods up to 180 days of age in hot weather climates. Two curing techniques were tested in this study in hot weather climates: (i) the specimens were submerged in a water container inside lab conditions and (ii) the specimens were left outdoors uncured until the day of the test. The fresh properties (slump test) and hardened properties (i.e., compressive, splitting tensile, and flexural strength), as well as water absorption, sorptivity, and microstructure (thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy), were evaluated experimentally. At age 180 days, application of the InC technique preserved compressive strength in the range of 74.5–85.8 % versus SuC for all replacement levels; meanwhile, this technique preserved splitting tensile and flexural strengths in the range of 86.8–93.1 % and 77.0–90.1 %, respectively. Utilizing VPD improved the permeability qualities by decreasing the water absorption ratio compared with the control specimen at all test ages. Despite the decrease in the hardened concrete characteristics, the application of InC achieves acceptable results compared with the amount of water that will be saved, especially in hot weather.

Thermally treated coal mining waste as a supplementary cementitious material – Case study from Bogdanka mine, Poland

The presented study deals with the comprehensive analysis of coal gangue from the Bogdanka mine (Lubelski Węgiel „Bogdanka" S.A.) in terms of its properties in both raw and activated states, and with the evaluation of the functional parameters of blended cement pastes containing 10 wt%, 15 wt%, and 20 wt% of thermally treated mining waste. The assessment of the raw material included chemical, physical, mineralogical, and morphological characterization, thermogravimetry, and pozzolanic activity tests. The motivation for the research was the intention to utilize a significant amount of waste from the Bogdanka mine with low additional energy consumption for processing. For this purpose, the temperature of 600 °C was chosen for its thermal activation based on the simultaneous thermal analysis (STA) measurement. The activated coal gangue was tested in the same way as the raw materials and then applied in the blended cement pastes as a partial cement substitute. The cement pastes were evaluated in the fresh state (flow table test), and also at the age of 7, 28, and 90 days. The structural, microstructural, mechanical, and hygric parameters were investigated and compared with the plain cement paste. Furthermore, the development and rate of the pozzolanic reaction were studied using simultaneous thermal analysis with mass spectrometry (STA-MS), X-Ray diffraction (XRD), isothermal calorimetry, and assessment of strength activity index (SAI). The performed analyses gave evidence of the pozzolanic activity of thermally activated coal mining waste (ACMW) from the Bogdanka mine and its effectiveness in cement blends. The slightly dropped hydration degree was later compensated by prolonged curing time and progress in the pozzolanic reaction. The blending of Portland cement with the examined ACMW did not negatively affect the rheology and setting time of fresh blended pastes. Considering the hardened cement blends' structural, microstructural, and mechanical parameters, ACMW can be safely used as a part of a PC-based blended binder for up to 20% replacement of cement mass.

Engineering properties of ultra-high strength concrete containing sugarcane bagasse and corn stalk ashes

Agricultural countries suffer from growth problems of agricultural waste ash (AWA). This research paper studies the use of AWA as a partial substitute for cement to produce ultra-high-strength concrete (UHSC). This paper also investigates the effect of using sugarcane bagasse ash (SBA) and corn stalk ash (CSA) on the properties of UHSC. Residues from the combustion process of agricultural wastes are utilized as a pozzolanic material inserted as a partial substitute for cement for UHSC production. The replacement rates of cement by the SBA were 10%, 20%, and 30% of the mass, whilst those of cement by the CSA were 2%, 4%, 6%, and 8% of the mass. The effects of SBA and CSA on workability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity on UHSC properties were investigated. In addition, the effects of SBA and CSA on resistance to chloride ion penetration and water sorptivity and permeability in UHSC were investigated. The investigations showed impressive results. That is, producing UHSC with respective compressive and flexural strengths of more than 205 and 27 MPa is possible when 24% of cement mass replacement by AWA (SBA 20% + CSA 4%) is conducted at the test age of 28 days. The lowest permeability is achieved with 38% of cement mass replacement by AWA (SBA 30% + CSA 8%) of 140 coulombs and 0.95 (cm/sec) for chloride and water permeability, respectively.

ПОЛУЧЕНИЕ СМЕШАННЫХ КОМПОЗИЦИОННЫХ ЦЕМЕНТОВ НА ОСНОВЕ ФЕРРИТНОГО КЛИНКЕРА

The possibility of using ferritic clinker as a component of binders with special performance properties is considered. Such types of cements can solve the problems of providing the construction industry with high-strength, resistant to external aggressive effects and relatively cheap binders. However, the mechanism of hardening and curing of cement stone obtained by using ferritic clinkers is complicated and depends on a number of parameters.&#x0D; It was found that the greatest thermal effect (more than 70%) during the hydration of the resulting ferritic clinker with the introduction of various additives (lime and gypsum stone) is achieved up to 4 hours from the moment the binder compositions are mixed by means of a calorimetric analysis carried out during the hydration of the developed special binder compositions. That corresponds to the course of the induction period of hydration of the used Portland cement, at the time of the occurrence of primary contacts between crystalline hydrates and sufficient mobility of the cement mass. In this time interval, the strength of the cement stone is not high enough and the produced iron-containing hydration products are able to fill the space of the cement matrix, making it more dense and less defective. &#x0D; The formation of iron-containing crystalline hydrates from ferritic clinker can proceed in several stages: hydrolysis of dicalcium ferrite at the initial stage of the reaction and further interaction of its products with portlandite in the period from 7 to 14 days from the moment of mixing the binder compositions. The main crystalline hydrates formed from ferritic clinker are iron-bearing ettringite and hydrogarnet.&#x0D; The study of the physical and mechanical characteristics of cement stone showed that the optimal content of ferritic clinker in the composition of the binder compositions is 5%. With a given quantity, the strength of the cement stone in compression and bending exceeds that of the control sample by 11.5%. The input of 15 and 30% ferritic clinkers into the composition of special binders reduces the strength characteristics by 15-20%.

Effect of Substitution of Cement by Mineral Powders on the Physicomechanical Properties and Microstructure of Sand Concretes

The approach that contributes to the development of eco-materials in construction is the use of mineral powders, which can improve mechanical properties and reduce cement consumption. This article aims to study the effect of substitution by mass of cement with mineral powders on the physicomechanical properties and microstructure of sand concretes. The used mineral powders are A: the limestone, B: the natural pozzolan, C: the hydraulic lime, D: (1/3 limestone + 1/3 natural pozzolan + 1/3 hydraulic lime), and E: (1/2 natural pozzolan + 1/2 hydraulic lime). The studied percentages are 5%, 10% and 15%, in both separated and combined states. The studied properties are workability, compressive strength, the elasticity modulus in compression, shrinkage and microstructure analysis. The objective is to target the optimal percentage of the substitution of cement with mineral powders, which ensures the best compromise between the main properties of the studied sand concretes. The obtained results show that the optimal percentage is in favor of the substitution of cement by 10% D (1/3 limestone, 1/3 natural pozzolan and 1/3 hydraulic lime). Even the 15% of mineral powder D, presented similar performances compared to the sand concrete (without mineral powders). Finally, in the context of the development of eco-materials, it should be noted that the 10% D and 15% D (1/3 limestone, 1/3 natural pozzolan and 1/3 hydraulic lime) contribute to decrease the use of cement and consequently to reduce of CO2 emissions.

Effect of nanosilica on fiber pullout behavior and mechanical properties of strain hardening ultra-high performance concrete

The bond properties between the fiber and matrix are a critical factor that affects the tensile properties and toughness of fiber-reinforced cementitious composites. This research aims to provide an effective method to improve the tensile properties of ultra-high performance concrete (UHPC) with strain hardening characteristics. The compressive, flexural, and tensile behavior was measured on UHPC with two geometric configurations of steel fibers and four nanosilica (nano-SiO2) mass fractions (0/1/3/5 wt% substitution rate of cement mass). The pull-out load-slip responses of steel fibers were also captured. In particular, determined the effect of fiber slip response on tensile properties of UHPC, then calculate elastic, strain hardening, and softening tensile parameters. Furthermore, the SEM, EDS, MIP, and XRD tests were used to reveal the enhancement mechanism of interfacial bonding performance and mechanical properties. The results show that the compressive and flexural strength peaks at 3 wt% of nanosilica, owing to nanosilica effectively ameliorating the pore structure and promoting the hydration process of the matrix. While the fiber pullout behavior and tensile properties show better performance at 5 wt% associated with increased hydration products attached to the fiber surface and more severe scratches after being pulled out. Notably, the addition of nanosilica endows strain hardening properties to UHPC containing straight fibers as well as increases the tensile toughness of UHPC containing hooked fibers due to the reinforcement of the matrix tunnel surrounding the steel fibers.

Similar ratio experiment and characteristic analysis of quasi-sandstone

The stability control of surrounding rock in deep roadway is becoming more and more difficult, and grouting reinforcement support has become the mainstream of roadway control. In order to obtain the ratio of quasi-sandstone material corresponding to the grouting body, this paper uses river sand as aggregate, cement and gypsum as cementing agent, retarder and defoamer as additives, and carries out orthogonal proportioning tests with three influencing factors: water-binder ratio (ratio of water to mass of cementing agent), gypsum-cement ratio (ratio of gypsum to mass of cement) and binder-aggregate ratio (ratio of cementing agent to aggregate mass), and compares and analyzes the sensitivity of each factor on the density, compressive strength, tensile strength, elastic modulus, Poisson’s ratio, longitudinal wave velocity, elasticity index and brittleness index of quasi-sandstone material. The results show that 1) the Water-binder ratio has the greatest effect on the sensitivity of material compressive strength, tensile strength, elastic modulus, Poisson’s ratio and longitudinal wave velocity; the gypsum-cement ratio has the greatest effect on the sensitivity of material deformation index and brittleness index; the binder-aggregate ratio has the greatest effect on the sensitivity of material density. 2) Reducing the Water-binder ratio can improve the density, compressive strength and tensile strength of the material; reducing the paste ratio can improve the modulus of elasticity, Poisson’s ratio and longitudinal wave speed of the material; as the gypsum-cement ratio increases, the deformation index first decreases and then increases and then decreases; as the binder-aggregate ratio increases, the brittleness index first increases and then decreases and then increases. 3) The empirical equations between physical and mechanical properties of sandstone-like materials and Water-binder ratio, gypsum-cement ratio and binder-aggregate ratio were established based on multiple linear regression analysis, and more reasonable material ratios were quickly obtained by physical and mechanical parameters of materials. The results of the study provide theoretical references for similar material simulation tests for quasi-sandstone grouting.

Improvement Mechanism of the Mechanical Properties and Pore Structure of Rubber Lightweight Aggregate Concrete with S95 Slag

This paper used natural pumice from the Inner Mongolia region as coarse aggregate to produce a lightweight concrete mix with a 3% rubber particle (20 mesh) content and dissimilar slag contents (0%, 5%, 10%, 15%, 20%, 25%, and 30%). It measured the compressive strength in five periods (3, 7, 14, 21, and 28 d). It also observed the development of the microstructure and measured the air content and pore distribution of the concrete using environmental scanning electron microscopy and nuclear magnetic resonance. A microtest combined with macroscopic mechanical experiments were used to analyze the influence on the mechanical properties of the rubber lightweight aggregate by the content of the S95 slag. The results showed that slag can improve the microstructure of rubber lightweight aggregate concrete. It hydrated the products, optimized the porous structure, and enhanced the compressive strength of the rubber lightweight aggregate concrete at 28 days, with excellent results regarding the air entraining. The best compressive strength of the rubber powder lightweight aggregate concrete at 28 days was when the content of the slag was 15%. An Atzeni pore-structure–strength model was introduced that contained a cement mass fraction. The results of the fitting indicate that the pore structure located at 0.1~1 μm had a marked influence on the mechanical properties of the rubber powder concrete.

The Influence of Nano-Silica on Some Properties of Light Weight Self-Compacting Concrete Aggregate

Lightweight concrete (LWC) has been used successfully in building constructions for many years due to its physical properties and its lightweight with high thermal insulation and durability. Recently, this work was done on a new type of concrete: lightweight self-compacting concrete (LWSCC) that combines the feature of lightweight and self-compacting concrete simultaneously. In this study, light expanded clay aggregate (LECA) was used as coarse aggregate in (LWSCC) mixtures, using nano-silica as a partial replacement of cement with three percent (0.5, 0.75, and 1%) by mass of cement. They were tested to evaluate these values of fresh characteristics through slump flow time and diameter, L-box, and segregation tests. The results of the fresh concrete tests showed a decrease in the workability of the concrete in the mixtures containing nano-silica due to the increase in fine materials in the mixture. The effects of nano-silica on the hardened properties of (LWSCC) such as compressive strength, flexural strength, splitting tensile strength, oven-dry density, and scanning electron microscopy (SEM), have improved. The mixtures containing nano-silica were investigated and compared with the reference mixture, where the results of the tests showed a significant improvement in the mechanical properties by (17.35, 16.27, 11.73, and 3.82%) for each of the compressive strength, flexural strength, splitting tensile strength and oven dry density respectively. In the presence of nano-silica, the replacement percentage of 1% recorded the best results in all tests at 90 days of curing.