Amount Of Cementitious Materials Research Articles

Remediation of grassland subsidence and reduction of land occupation with tailings backfill technology: a case study of lead-zinc mine in Inner Mongolia, China

The mining industry provides essential mineral resources for human society’s development. However, this industry generates a large quantity of waste material while rapidly extracting valuable elements from ore, such as processed tailings. The existence of mined voids will cause surface subsidence, and the surface stockpiling of tailings and waste rocks occupy a large amount of land and the risk of Tailings Storage Facility (TSF) failure. This paper proposes tailings backfill technology to mitigate surface subsidence and provides an alternative disposal method for tailings generated during ore extraction. Tailings backfill technology prepares the slurry by adding a certain amount of cementitious material into the tailings and transporting it to the underground goaf through a pipeline. The backfill slurry could then gradually build up its strength during the hydration of. Cementitious material. A case study of a lead-zinc mine in the Inner Mongolia Autonomous Region of China using tailings backfill technology was introduced in detail to solve the problems of grassland collapse caused by mine excavation and environmental damage due to tailings disposal. Spread test and rheological test were carried out to study the flow characteristics of filling slurry and the uniaxial compressive strength (UCS) of backfill was tested as well. The result illustrates that the spread of the filling slurry with a solid content between 72% and 76% and cement-tailings ratio between 1:4 and 1:8 is greater than 14 cm, and the UCS of backfill is above 1 MPa. The research shows that the tailings backfill technology recycles tailings waste while mitigating surface grassland subsidence and land occupation of waste disposal. Tailings backfill technology can significantly reduce tailings discharge or even achieve no discharge. A leaching test for heavy metal element classification of the backfill sample was carried out. The results show that the heavy metal detection indicators meet the environmental protection standard requirements and will not cause secondary environmental pollution. Therefore, tailings backfill technology can realize green and efficient management of mine waste and has great application and promotion prospects.

A high‐strength concrete resistant to elevated temperatures using steel slag aggregates

AbstractThis paper investigates high‐strength concrete (HSC) exposed to high temperatures using the full replacement of natural aggregates with steel slag. Polypropylene (PP) and steel fibers are used as reinforcements, and the effects of calcium aluminate cement and ordinary cement on the mechanical properties of this concrete are compared. A total of 81 cylindrical specimens of 100 × 200 mm and 81 prism specimens of 100 × 100 × 350 mm were made using different amounts of cementitious materials (cement and silica fume) of 450, 500, and 550 kg/m3, with constant water‐to‐cementitious materials ratio of 0.28. The present results revealed that the HSC made with steel slag aggregates and calcium aluminate cement reinforced with steel fibers, had the greatest compressive strength of 84 and 50 MPa at temperatures of 20°C and 800°C, respectively; and flexural strength of 7.9 and 4.5 MPa, respectively, at the same temperatures. Similar HSC specimens constructed with ordinary cement, on the other hand, performed better at 400°C. Moreover, the flexural strength of the samples placed at temperatures of 400°C and 800°C decreased by 28% and 48%, respectively, compared to the specimens at 20°C. Compared to specimens comprised of polypropylene fibers, the fracture energy and displacement of HSC with steel slag reinforced with steel fibers subjected to high temperatures were increased by approximately 100% and 60%, respectively.

Study on Early Shrinkage and Mechanical Properties of Concrete with Various Cementitious Materials

Due to the rapid development of industrialization, the recycling and utilization of industrial by-products have received extensive attention. In this paper, binary, ternary, and quaternary composite cementitious materials were prepared using steel slag, blast furnace slag, and fly ash, and the effects of different cementitious materials on concrete properties were explored. A variety of solid wastes were mixed, and batches of concrete with high mechanical properties and durability were prepared by adjusting the type and amount of cementitious materials used. A total of 15 batches of concrete were prepared and tested for compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and drying shrinkage. The test results show that a fly ash, blast furnace slag powder, and steel slag powder ratio of 1:1:2 produces a concrete with the best mechanical properties. Among them, the cube compressive strength can reach 62.9 MPa, the splitting tensile strength is 5.7 MPa, the axial compressive strength and elastic modulus are increased, the early shrinkage is small, the growth rate is slow, and the 28d concrete shrinkage rate is 4.87 × 10−4. This new type of green mixed concrete can not only control production costs, but can also reduce environmental impact and decrease carbon dioxide emissions.

The Influence of Fly Ash Content on the Compressive Strength of Cemented Sand and Gravel Material

Cemented sand and gravel (CSG) material is a new type of dam material developed on the basis of roller compacted concrete, hardfill, and ultra-poor cementing materials. Its main feature is a wide range of sources of aggregate (aggregate is not screened but by simply removing the large particles it can be fully graded on the dam filling) and low amounts of cementitious materials per unit volume. This dam construction material is not only economical and practical, but also green and environmentally friendly. There are many factors affecting the mechanical properties of CSG materials, such as aggregate gradation, sand ratio, water content, water–binder ratio, fly ash content, admixture content, etc. Based on the existing research results of the team, this paper focuses on the influence of fly ash content on the compressive strength of CSG materials. Through a large number of laboratory measured data, we found: (1) The compressive strength law of materials at different ages; the compressive strength of CSG material at age 90 d is generally 10%~30% higher than that at 28 d, and it is proposed that 90 d or 180 d strength should be used as the design strength in the design of CSG material dam; (2) There is an optimal value of fly ash content in CSG materials: when the fly ash content is 50% of the total amount of cementitious materials (cement + fly ash), the fly ash content is defined as the optimal content, and the test data are verified by regression analysis. The discovery of an ‘optimal dosage’ of fly ash provides an important reference for the design and construction of CSG dams.

Study of the Properties of Full Component Recycled Dry-Mixed Masonry Mortar and Concrete Prepared from Construction Solid Waste

Solutions are needed to solve the problem of a large amount of construction solid waste and a shortage of natural aggregate (coarse and fine aggregates). In this paper, simple-crushed coarse aggregate (SCRCA) and simple-crushed fine aggregate (SCRFA) were obtained by simple-crushing of construction solid waste. On this basis, SCRCA and SCRFA were treated with particle-shaping to obtain particle-shaping coarse aggregate (PSRCA) and particle-shaping fine aggregate (PSRFA), and the recycled powder (RP) produced in the process of particle-shaping was collected. Under the condition of a 1:4 cement-sand ratio, RP was used to replace cement with four substitution rates of 0, 10%, 20%, and 30%, and dry-mixed masonry mortar was prepared with 100% SCRFA, PSRFA, and river sand (RS). The basic and mechanical properties and microstructure of hydration products of dry-mixed mortar were analyzed, and the maximum substitution rate of RP was determined. Under the condition that the amount of cementitious material is 400 kg/m3 and the RP is at the maximum replacement rate, three different aggregate combinations to prepare concrete are the 100% use of SCRCA and SCRFA, PSRCA and PSRFA, and RS and natural aggregate (NCA); the workability, mechanical properties, and aggregate interface transition zone of the prepared concrete were analyzed. The results show that when the replacement rate of RP is less than 20%, it has little effect on the properties of products. The performance of PSRCA and PSRFA after treatment is better than that of SCRCA and SCRFA. Under different RP substitution rates, the performance of dry-mixed mortar prepared with PSRFA is very close to that prepared with RS. The performance of recycled concrete prepared with PSRCA and PSRFA is also very close to that of products prepared with NCA and RS. The failure morphology of PSRCA and RSRFA concrete is also similar to that of NCA and RS concrete.

Effect of Assembly Unit of Expansive Agents on the Mechanical Performance and Durability of Cement-Based Materials

This paper studies the influence of assembly unit of expansive agents (CaO and calcium sulphoaluminate) on the limited and free compressive strengths, the limited expansion rate, carbonation resistance, chloride ion penetration resistance and corrosion resistance of reinforcement concrete. The dosages of expansive agent were 0%, 3%, 6%, 9%, and 12% by the total amount of cementitious materials. Two kinds of mineral admixture (blast furnace slag and fly ash) were applied in this study. Results show that suitable dosage (lower than or equal to 9%) of double expansion agent with a large amount of mineral admixtures can improve the limited and free compressive strengths. However, when the dosage of the double expansion agent is higher than 9%, the addition of the double expansion agent leads to the reduction of limited and free compressive strengths. The variation of the limit expansion rate reaches the maximum value when the curing age is 14 days. The increasing addition of expansive agents and lower water-binder ratio demonstrate positive effect on the limited expansion rate. Concrete with 60% mineral admixtures (fly ash and ground granulated blast furnace slag) shows lower limited expansion rate and higher compressive strength than the concrete with 50% mineral admixtures. Finally, the incorporation of double expansion agent can improve the resistance to carbonation, chloride ion penetration resistance, anti-corrosion of steel bars and mechanical strengths (the limited and free compressive strengths).

Experimental investigation of cracking behaviors of ductile and brittle rock-like materials

The cracking characteristics of ductile rocks were studied by similar materials with sand, barite, epoxide resin, polyamide, silicone rubber and alcohol, while the cracking characteristics of brittle rocks were investigated by similar material with sand, barite, rosin and alcohol. In this paper, to enhance the application range of the rock-like materials in the field of geotechnical engineering model tests, the values of the elastic modulus and the compressive strength of the artificial rock-like materials are changed in a wide range by adjusting the amount of cementitious materials (epoxide resin, polyamide, rosin, etc). The elastic modulus, compressive strength and cracking characteristics were obtained from the complete axial stress–strain curves of the specimens made of similar materials, which were cast using the different mixture ratios. These experimental data can provide quantitative investigation on mixture ratios of similar materials of rocks to model the geotechnical engineering. Furthermore, the effect of mixture ratios on mechanical properties and crack propagation pattern of specimens were also investigated by the specimens with pre-existing flaws under uniaxial compressive tests

Experimental Investigation of the Dynamic Characteristics of Treated Silt Using Lignin: Case Study of Yellow River Flood Basin

Silt is widely distributed in North China Plain, especially in the Yellow River flood basin. Unfortunately, untreated silt cannot be directly used as a subgrade filler. Therefore, it is of great practical significance to explore the reinforcement of silt in the Yellow River flood basin. To solve this problem, the dynamic characteristics of silt added with different proportions of lignin were studied. The correlation among lignin content, curing time, dynamic shear modulus, and damping ratio of the improved soil was tested. The results showed that the dynamic strength and shear modulus can be effectively improved by adding lignin. The optimal lignin content for the dynamic strength and shear modulus was 5%. To understand the microscopic mechanism of lignin-treated silt, scanning electron microscopy (SEM) was performed on lignin samples. The SEM results showed that with an increase in lignin content, a certain amount of cementitious materials was formed in the soil. These cementitious materials wrap up the soil particles and connect the fine soil particles to form larger aggregates. The research results can provide a reference to further improve the physical and mechanical properties of the silt in the Yellow River flood basin, and this study is instructive.

Strength Prediction Model of High Strength Fly Ash Concrete Based On Mixed Kernel Function

In this paper, the proportion of fly ash in cementitious material, the amount of cementitious material and the ratio of water to cement are selected, and the rough set theory is used to process the data. A mixed kernel function support vector machine prediction model with conditional attribute as input and decision attribute as output is established to explore the influence of three factors on the strength of high strength fly ash concrete. The prediction model with high prediction accuracy is selected for optimization. According to the existing test data, the variation law of concrete strength with proportioning parameters is summarized.

Research on C30 Concrete Mix Proportion in Guangdong Province

The reasons of C30 concrete bleeding in winter in Guangdong province were studied by collecting the concrete mix proportions of C30 concrete mixing plants in Guangdong, Fujian, Henan, Hunan, Chongqing and Shaanxi regions, the difference between the concrete mix proportions in Guangdong and other regions was investigated. Based on the representative concrete mix proportion in Guangdong province, the concrete bleeding water test was carried out, and the correlation between the amount of different cementing materials and the bleeding rate was investigated. The results showed that compared with other regions, the C30 concrete mix proportion in Guangdong has the lowest total cementitious material, which made it more prone to bleeding. The amount of slag powder and the total amount of cementitious materials have a high correlation with the bleeding rate. With the increase of the amount of slag powder and the total amount of cementitious materials, the bleeding rate decreases.

An Evolutionary-Based Prediction Model of the 28-Day Compressive Strength of High-Performance Concrete Containing Cementitious Materials

Abstract High-performance concrete (HPC) is a class of concretes that may contain more cementitious materials other than portland cement, such as fly ash and blast furnace slag, in addition to chemical admixtures, e.g., plasticizers. Strength, durability, and rheological properties of the normal concrete are enhanced in HPC. The compressive strength of HPC can be considered as a key factor to identify the level of its quality in concrete technology and the construction industry. This parameter can be directly acquired by experimental observations. However, testing methods are often time consuming, expensive, or inefficient. This article aims to develop and propose a new mathematical equation formulating the compressive strength of HPC specimens 28 days in age through a robust artificial intelligence algorithm known as linear genetic programming (LGP) using a valuable experimental database. The LGP-based model proposed here can be used for manual calculations and is able to estimate the compressive strength of HPC samples with a good degree of accuracy. The performance of the LGP model is confirmed through comparing the results with those provided by other models. The sensitivity analysis is also conducted, and it is concluded that the amount of cementitious materials, such as cement and furnace slag, have more influence than other variables.

Study on the stress relaxation properties of self-compacting concrete under restrained autogenous shrinkage

The development of internal stress and stress relaxation induced by restrained autogenous shrinkage of self-compacting concrete (SCC) with different water to binder ratios and different amount of cementitious materials was investigated. Test results at more than 100 days showed that the free autogenous deformation expands within 1 day and then shrinks rapidly from 3 days to 7 days, after that, the autogenous shrinkage grows slowly and steadily. The induced stress in the restrained autogenous shrinkage also had the similar law; the stress relaxation of restrained autogenous shrinkage mainly developed in the early ages within 7 days, and then growth of the stress relaxation was almost stagnant. Stress relaxation rate of self-compacting concrete increased with the increase of cementitious content, and it increased significantly with the increase of water to binder ratio.

Ultrafine GGBS and calcium nitrate as concrete admixtures for improved mechanical properties and corrosion resistance

This work reports the modification of ordinary Portland cement with ultrafine ground granulated blast furnace slag (GGBS) as a mineral admixture and calcium nitrate as a chemical admixture and examines how mechanical and corrosion properties are improved by this modification. Ultrafine GGBS with average particle size of 4–6 μM was introduced as a replacement mineral admixture (10%) to ordinary Portland cement while calcium nitrate was introduced as a chemical admixture at 2% amount of cementitious material, in the preparation of concrete. X-ray diffraction studies on powdered concrete showed that the amount of silica in the concrete increases with the introduction of GGBS. Calcium hydroxide was converted to calcium silicates. Ultrafine GGBS reduced the workability and water absorption and increased the compressive strength of the concrete (18%) and the bond strength of the steel rebar (45%). Adding calcium nitrate further reduced water absorption of the concrete but improved workability, compressive strength (32%) and bond strength (131%). The pH of the concrete powdered solution became more alkaline with the replacement of ultrafine GGBS and addition of calcium nitrate. Free chloride content dropped by 39% and 65%, respectively, with the introduction of GGBS and nitrate. Corrosion behaviour of the concrete specimens were studied using measurement of open circuit potentials, linear polarization resistance and Tafel polarization in an accelerated corrosion medium of 3.5% NaCl and 1 M sulphuric acid. Corrosion potential and current of the control specimens decreased with time for 40 days after which an increase was observed. Ultrafine GGBS shifted the corrosion potential in the cathodic direction, indicating retardation of the cathodic reaction (ex. oxygen reduction). Calcium nitrate, on the other hand, shifted the corrosion potential anodically by promoting the formation of a passive film of iron(III) hydroxide on the steel surface. Corrosion currents in GGBS and nitrate-modified concrete decreased by 200-fold compared to the control specimen on the first day, and by 480-fold on the 50th day (150-times smaller than the specimen modified with GGBS alone). Finally, scanning electron microscopy images of the corroded rebar at the end of 50th day indicate that pitting and intergranular corrosion occurs, with its extent reduced significantly by the introduction of admixtures. These results demonstrate that ultrafine GGBS and calcium nitrate as admixtures enhance the mechanical properties of concrete and reduce the corrosion of rebar.

Rapid-hardening controlled low strength materials made of recycled fine aggregate from construction and demolition waste

Rapid-hardening controlled low strength material (CLSM) containing recycled fine aggregate from construction and demolition (C&D) waste was prepared with the sprayed concrete accelerator. Eleven mixtures were made with different accelerator-to-binder (A/B), water-to-solid (W/S) and binder-to-recycled fine aggregate (B/R) ratios. The workability (flowability and bleeding rate) of fresh mixture and the mechanical properties (early strength, long-term strength and dynamic elastic modulus) of hardened material were tested. The results show that adding (20 ∼ 50%) accelerator reduces the bleeding rate of CLSM by 48.8 ∼ 84.6%, with no significant effect on the flowability. Improved flowability of CLSM can be achieved by increasing the W/S or B/R ratio, with increased or reduced bleeding rate, respectively. The optimal A/B ratio for best early strength development is 40%, with the early hour strength (2 ∼ 4 h) up to 0.41 ∼ 0.79 MPa. When A/B ratio is held constant, the early strength of CLSM is affected by the amount of cementitious materials and the actual content of free water. An accurate predictive model for the long-term strength of CLSM was established through regression analysis, in which three control parameters are considered. A power function relationship between the compressive strength and the dynamic elastic modulus is also established. Dynamic elastic modulus can thus serve as an indicator for evaluation of the mechanical properties of CLSM.

A Case Study On Zoning And Construction Of Roller-Compacted-Concrete Gravity Dams

In order to make full use of the concrete strength, reduce the amount of cementitious materials and simplify the temperature control measures, a roller compacted concrete (RCC) dam needs to be zoned reasonably in consideration of locations and working conditions. Taking the RCC gravity dam of Wuxikou hydropower project in Jiangxi province, this article specifies the zonation design, the problems encountered during construction stage and the corresponding measures. The results indicate that the zonation and the construction schemes of the RCC gravity dam can greatly reduce the amount of cementitious materials, improve the level of mechanization in construction, and thus accelerate the construction progress, reduce the project cost. It not only ensures the quality and safety of the project, but also achieves obvious economic benefits. It can be an important reference for zonation design and construction of similar projects.

Influence of Concrete Synergist on Performance of Stone Chip Concrete

The concrete synergist can reduce the amount of cementitious material, keep the performance of the concrete not reducing or even improving. By adjusting the ratio, effect of concrete synergist on the properties of stone chip concrete was studied, results showed that in reducing the dosage of cement, concrete synergist can also effectively improve the working performance of concrete. The early strength of concrete adding synergist is inferior as that of the base, after the later the strength will increase slightly. Adding synergist, shrinkage of concrete is larger, the contraction slows after later period. By adding concrete synergist, concrete electric flux declines slightly, which is beneficial to anti permeability of concrete. Concrete synergist can optimize the microstructure of concrete and increase the density of concrete. The application of the concrete synergist is feasible and can be used to improve the efficiency of the materials.

Study on the Expansion of a Cement-Based System Containing Sap Polymer and Supplementary Cementing Materials

In this paper, the addition of admixed superabsorbent polymer (SAP) improved the microstructure and durability-related properties in a cement-based system with supplementary materials. This is an important issue in real construction projects when good durability properties are required. This study investigates the effect of SAP on the systems using cement replacement by fly ash and silica fume considering the strength properties and durability properties of paste under sulfate attack of cement-based system. The replacement considered in the study was of 10% silica fume and 20% fly ash in each case, the dosage of SAP was 0.25% of the total amount of cementitious material. The results showed that the addition of SAP in the cement-based system improved the compressive strength and reduced expansion to sulfate attack. Scanning electron micrographs showed that utilization of fly ash with silica fume and silica fume with SAP resulted in a much denser microstructure, thereby, leading to an increase in compressive strength and lower expansion under sulfate attack.

Use of adiabatic calorimetry for performance assessment of concretes

Modern concrete construction involves the use of a variety of special concretes. While the design of such concretes accounts for the achievement of characteristics such as high strength, toughness, flowability, shrinkage compensation and so on, one aspect that is not sufficiently addressed is the heat evolution in such concretes. This can be of particular importance when the concrete mix uses a large amount of cementitious materials. Furthermore, heat development can also be a major problem for regular mixes when the concrete is not properly optimised for the composition and content of the binder. This paper reports on an extensive experimental investigation, using an adiabatic calorimeter that was developed in-house, on heat development in two categories of concretes – special high-strength concretes with compressive strengths of 60–100 MPa and ordinary regularly used concretes with strengths of 30–50 MPa. The relevant hardened properties of the concretes were also evaluated and compared. The results indicate that heat development is a serious issue in high-strength concretes, while suitable selection of materials for ordinary concretes can lead to a major reduction in the level of heat evolution in the early stages.

A comparison of strength and elastic properties between conventional and lightweight structural concretes designed with expanded clay aggregates

Properties such as compressive strength, modulus of elasticity (MOE), Poisson’s ratio and the ductility of lightweight aggregate concrete (LWAC) mixtures were investigated, and the results obtained were compared with conventional concrete (CC) mixtures with similar design characteristics. For this purpose, LWAC mixtures were casted using lightweight expanded clay (EC) aggregates with different unit weight properties. Dry unit weights of LWAC mixtures changed approximately between 1640kg/m3 and 2050kg/m3. To express the effect of matrix strength on the determined properties, concrete mixtures with different matrix strengths were designed by keeping the total aggregate volume constant. For this purpose, the water to cementitious material ratio and the amount of cementitious materials were changed. Results have shown that, depending on the unit weight of concrete, the compressive strength of LWAC mixtures varied between 20MPa and 70MPa. Compared with CC mixtures, the elastic properties and ductility of LWAC mixtures changed significantly. Within the same compressive strength range, LWAC mixtures showed remarkable reduction in MOE and more brittle behavior compared with CC mixtures. Poisson’s ratios of the LWAC and CC mixtures, on the other hand, produced similar values. A new model for predicting the MOE of such concretes is also suggested.

A testing procedure for predicting strength in artificially cemented soft soils

It is globally recognized that soft soils will have low strength and high compressibility and that under reduced loads might collapse or suffer large displacements. In order to reduce settlements and increase bearing capacity of structures built on such soils, their stabilization using cementitious materials such as Portland cement and/or quicklime (increasing strength and stiffness) is an efficient technique used worldwide. The focus of this research is to present and check the accuracy of a new testing procedure to evaluate strength gain in very soft soils when using cementation as a means of improvement. This testing procedure was intended to fasten acquiring strength results in artificially cemented soft soils. In short, in the proposed procedure the force applied to embed a flat base rod into a soil mass is measured by using high resolution load rings. The proposed flat base rod embedding test was shown to be adequate for evaluating the gain in strength of cemented soils. Results of embedding flat base rod strength have unique linear relations with both unconfined compressive strength and splitting tensile strength, being independent of type and amount of cementitious material (Portland cement and/or quicklime), as well as of the curing time period. The wrap up of present studies is that the developed testing procedure can be used as a substitute of unconfined compression and splitting tensile tests as a dosage test, being easier to mold specimens (might be molded in the field) and faster in acquiring strength results (can be carried out in a bucket filled with soil and the cementitious material, in which will be attached to the load ring) in artificially cemented soft soils.