scholarly journals Performance of Coal Gangue-Based Cemented Backfill Material Modified by Water-Reducing Agents

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Yuxia Guo ◽  
Peng Wang ◽  
Guorui Feng ◽  
Tingye Qi ◽  
Guoyan Liu ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Yield Stress ◽  
Reducing Agents ◽  
Plastic Viscosity ◽  
Coal Gangue ◽  
Bleeding Rate ◽  
Backfill Material ◽  
Slump Flow ◽  
Cemented Backfill

Coal gangue-based cemented backfill material (CGCBM) is developed for backfilling the goaf in coal mines. As fresh CGCBM slurry is generally transported into underground openings through a pipeline, and after hardening, it plays the role of supporting the overlying strata. The fluidity, stability, and mechanical (compressive strength) of CGCBM become the most important properties. Adding water-reducing agents (WRAs) is considered to improve the fluidity, stability, and mechanical properties of CGCBM, but there is a risk of increased bleeding. So, two types of WRA (naphthalene series (WRA1) and poly carboxylic acid (WRA2)) are used at different contents (1.0%-2% for WRA1, 0.2%–0.6% for WRA2) by mass of binder. Slump, slump flow, yield stress, and plastic viscosity test are used to evaluate the fluidity properties of CGCBM after adding WRA. Bleeding rate test is used to evaluate the stability of CGCBM after adding WRA. Compressive strength is the most important factor in measuring the mechanical properties. SEM and XRD tests are used to analyse the mechanism of strength change. Results show that the slump, slump flow, and plastic viscosity increase after adding WRA, which reduces the yield stress and improves the fluidity. The bleeding rate increases with the increase of WRA content, leading to a decrease in stability. Adding WRA increases the compressive strength, and it increases first and then decreases with the increase of the content at the later stage. Considering the effects of WRA on the fluidity, stability, and compressive strength properties of CGCBM, the reasonable content of WRA1 and WRA2 is 1.5% and 0.4%, respectively. The research results provide guidance for the design and preparation of CGCBM with favourable performance in practical production.

scholarly journals Influence of Lightly Burned MgO on the Mechanical Properties and Anticarbonization of Cement-Based Materials

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 714
Author(s):  
Lin Wang ◽  
Chao Li ◽  
Chunxue Shu ◽  
Han Yong ◽  
Jianmin Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Shear Stress ◽  
Cement Paste ◽  
Plastic Viscosity ◽  
Expansion Rate ◽  
Cement Concrete ◽  
Slump Flow ◽  
Cement Based Materials ◽  
Curing Age

This study aims to study the influence of a lightly burned magnesium oxide (LBMO) expansion agent on the rheological properties (the slump flow, plastic viscosity and variation of shear stress) of cement-based materials. Four different mass contents (i.e., 0%, 3%, 6% and 9%) of LBMO were selected. The following compressive strength and expansion value of the corresponding cement concrete were tested. Cement concrete with two strength grades of 30 MPa and 50 MPa (C30 and C50) was selected. Results indicated that the addition of LBMO can effectively decrease the fluidity and increase the plastic viscosity of fresh cement paste. An optimum dosage (3%) of LBMO is the most advantageous to the compressive strength of cement concrete. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. Moreover, the incorporation of LBMO led to a reduction in the fluidity of the cement paste and an increase in plastic viscosity. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. It can be found that little difference exists in the compressive strength and the expansion rate of cement concrete with strength grades of 30 MPa and 50 MPa. Finally, the increased dosage of LBMO, curing age and compressive strength led to improving the carbonization resistance of cement concrete.

scholarly journals Evaluations of All-in-One, Polycarboxylate-Based Superplasticizer with Viscosity Modifying Agents for the Application of Normal-Strength, High-Fluidity Concrete

2021 ◽  
Vol 11 (23) ◽  
pp. 11141
Author(s):  
Tae-Woong Kong ◽  
Hyun-Min Yang ◽  
Han-Seung Lee ◽  
Chang-Bok Yoon
Keyword(s):  
Compressive Strength ◽  
Rheological Properties ◽  
Yield Stress ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Slump Flow ◽  
Different Types ◽  
Long Time ◽  
Normal Strength ◽  
Physical Phenomena

High fluidity concrete exhibits an excellent self-compacting property. However, the application of typical high-fluidity concrete is limited in the normal strength range (18~35 MPa) due to the large amount of binder. Therefore, it is important to solve these problems by adding a viscosity modifying agent (VMA) with a superplasticizer (PCE), which helps to improve the fluidity of the concrete. In addition, the rheology and stability of the concrete with VMA can be improved by preventing bleeding and segregation issues. Current studies focused on the physical phenomena of concrete such as the fluidity, rheological properties, and compressive strength of normal-strength, high-fluidity concrete (NSHFC) with different types of a polycarboxylate-based superplasticizer (NPCE). The obtained results suggested that the combinations of all-in-one polycarboxylate-based superplasticizers (NPCE) did not cause any cohesion or sedimentation even stored for a long time. The combination of three types of VMA showed the best fluidity (initial slump flow of 595~630 mm) without any segregation and bleeding, and the compressive strength at 28 days was also found to be the highest: 34–37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity and -4.4% lower yield stress than Plain.

scholarly journals Study on Mechanical Properties of PET Fiber-Reinforced Coal Gangue Fine Aggregate Concrete

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Yanlin Huang ◽  
An Zhou
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Plain Concrete ◽  
Coal Gangue ◽  
Fine Aggregate ◽  
Replacement Rate ◽  
River Sand ◽  
Aggregate Concrete

In recent years, with the rapid development of the construction industry, the demand for natural river sand has become increasingly prominent. Development of alternatives to river sand has become an interesting direction for concrete research. In this paper, coal gangue was proposed to replace part of the river sand to produce coal gangue fine aggregate concrete, while waste polyethene terephthalate (PET) bottles were used as raw materials to make PET fibers to improve the mechanical properties of coal gangue fine aggregate concrete. There were two parts of the test conducted. In the first part, the compressive strength of the gangue fine aggregate concrete cube, splitting tensile strength, axial compressive strength, and static elastic modulus were studied when the substitution rate of coal gangue increased from 0% to 50%. Referring to the equation of the full stress-strain curve of plain concrete, the stress-strain constitutive equation of coal gangue fine aggregate concrete was analyzed and studied. By comparing with plain concrete, it was found that the coal gangue concrete with a replacement rate of 50% had higher compressive strength and tensile strength, but its brittleness was significantly greater than that of plain concrete in the later stage. In the second part, by studying the effect of different PET fiber content on the mechanical properties of coal gangue fine aggregate concrete with a replacement rate of 50%, it was found that when the addition of PET fiber was 0.1% and 0.3%, not only were compressive strength, splitting tensile strength, static elastic modulus, and flexural strength of the gangue fine aggregate concrete effectively improved but also the brittleness of concrete can be significantly reduced. The study found that after adding 0.3% PET fiber, the coal gangue fine aggregate concrete with a replacement rate of 50% has better mechanical properties and less brittleness.

scholarly journals Fresh, Mechanical Properties and Impact Resistance Behavior of Eco-Friend Self-Compacted Concrete

2019 ◽  
Vol 22 (3) ◽  
pp. 208-212
Author(s):  
Sheelan M. Hama ◽  
Alhareth M. Abdulghafor ◽  
Mohammed Tarrad Nawar
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Flexural Strength ◽  
Polyethylene Terephthalate ◽  
Glass Powder ◽  
Impact Resistance ◽  
Waste Glass ◽  
Slump Flow ◽  
Waste Glass Powder ◽  
Self Compact Concrete

In this work, waste glass powder from broken windows and plastic fibers from waste polyethylene terephthalate bottles are utilized to produce an economical self-compact concrete. Fresh properties (slump flow diameter, slump Flow T50, V. Funnel, L–Box), mechanical properties (Compressive strength and Flexural strength) and impact resistance of self-compact concrete are investigated. 15% waste glass powder as a partial replacement of cement with five percentages of polyethylene terephthalate plastic waste were adopted: 0% (reference), 0.5%, 0.75%, 1%, 1.25% and 1.5% by volume. It seems that the flow ability of self-compact concrete decreases with the increasing of the amount of plastic fibers. The compressive strength was increased slightly with plastic fiber content up to (0.75%), about 4.6% For more than (0.75%) plastic fiber. The compressive strength began to decrease about 15.2%. The results showed an improvement in flexural strength and an impact on the resistance in all tested specimens’ content of the plastic fibers, especially at (1.5%) fibers.

scholarly journals Effect of polypropylene fibers on high strength mortar subjected to elevated temperature

2020 ◽  
Vol 156 ◽  
pp. 05010
Author(s):  
Muhammad Ridwan ◽  
Hu Liang Jun ◽  
Isamu Yoshitake
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elevated Temperature ◽  
Flexural Strength ◽  
Fiber Length ◽  
Heating Temperature ◽  
High Strength ◽  
Polypropylene Fibers ◽  
Slump Flow ◽  
Residual Mechanical Properties

This study focuses on the thermo-mechanical properties of mortar in the retrofitting cover of additional reinforcement for existing concrete structures. In addition, the residual mechanical properties of high strength mortar incorporating polypropylene fibers subjected to the effect of fiber length and the elevated temperature were investigated. Several experiments were conducted to determine the optimum mixture proportions of high strength mortar incorporating polypropylene fibers which had a slump-flow of 25–30 cm, compressive strength of 50 MPa or higher, and flexural strength of 4–8 MPa. Subsequently, an experiment was conducted by using high-strength mortar-blended polypropylene fibers with a length of 2 cm, and the ratio of fiber length to the diameter of cylinder mortar-specimens was 0.4. The experimental parameters were the weight volume of fibers (0 %, 0.5 %, 1 %, and 2%) and the heating temperature (100, 200 and 300 °C). The effect of the mixing parameters, including polypropylene length on compressive strength, slump-flow and the flexural strength of mortar were discussed. It is evident that fiber in the mortar cover influenced the initial and residual mechanical properties, such as elasticity, compressive strength, and Poisson’s ratio, of the mortar.

scholarly journals Effect of recycled coarse aggregate on the properties of C40 self-compacting concrete

2019 ◽  
Vol 28 ◽  
pp. 096369351988512 ◽  
Author(s):  
Yunyang Wang ◽  
Bingchen Zhao ◽  
Guang Yang ◽  
Yandong Jia ◽  
Lijun Yang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Modulus Of Elasticity ◽  
Coarse Aggregate ◽  
Lower Amount ◽  
Theoretical Formula ◽  
Self Compacting Concrete ◽  
Recycled Coarse Aggregate ◽  
Slump Flow ◽  
Experimental Values

The effect of recycled coarse aggregate (RCA) on the fresh and hardened properties of C40 self-compacting concrete (SCC) was investigated in this paper. The slump, T 500 (the time needed for SCC to spread into a round configuration with a nominal diameter of 500 mm), the slump flow and the flow time of fresh C40 SCC as well as the compressive strength and modulus of elasticity of hardened C40 SCC were studied. The modulus of elasticity of C40 SCC was calculated by theoretical formula, and the calculated values were compared with the experimental values. Mechanisms that effect on the C40 SCC properties at fresh and hardened states were also explored. The experimental results showed that the slump values of the C40 SCC are beyond 250 mm. The C40 SCC with RCA replacement content of 50% showed the highest slump value of 275 mm. All T 500 values of the C40 SCC are within 5 s. The slump flow of the C40 SCC slightly increases with the increase of replacement content of the RCA. In contrast, the compressive strength and modulus of elasticity of the C40 SCC slightly decrease with the increase of replacement content. The experimental values of modulus of elasticity are lower than that of the calculated values. Submerged in water before mixing of RCA leading to the slump flow of the C40 SCC increases with the increasing replacement content of the RCA. The old cement mortar attached to the RCA surface is the main reason that weakens the mechanical properties. The lower amount of coarse aggregate and the higher amount of cement paste attribute to the lower values of modulus of elasticity. This study implied that RCA can be effectively used in the production of C40 SCC without any significant sacrifice on workability and mechanical properties.

scholarly journals Rheology, Mechanical Properties and Porosity of Ternary Alkali-Activated Binders Based on Mining Mud Waste with Waste Glass and Metakaolin

CivilEng ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 236-253
Author(s):  
Abdelhakim Benhamouda ◽  
João Castro-Gomes ◽  
Luiz Pereira-de-Oliveira
Keyword(s):  
Mechanical Properties ◽  
Portland Cement ◽  
Yield Stress ◽  
Relative Yield ◽  
Rheological Behaviour ◽  
Waste Glass ◽  
Plastic Viscosity ◽  
Rheological Parameters ◽  
Alkali Activated Binders ◽  
Alkali Activated

Alkali-activated materials have the potential to replace Portland cement in certain applications. To better understand these binders’ properties, it is relevant to study their rheological behaviour at early ages, like in the case of Portland cement paste. There are already many studies on the rheological behaviour of these materials in the available literature, using fly ash, metakaolin, and ground granulated blast furnace slag as precursors. However, this study discusses the rheological behaviour, mechanical properties, and porosity of ternary alkali-activated binders based on mining mud waste, waste glass, and metakaolin. The precursor consisted of a volume mix of 70% of tungsten mining waste mud, 15% glass waste, and 15% of metakaolin. The activator was a combination of sodium hydroxide and sodium silicate solution. Five activator/precursor (A/P) ratios (0.37, 0.38, 0.39, 0.40, and 0.4) were studied. The result showed that the activator/precursor ratio affects the rheology of paste and their rheological behaviour fit the Bingham model. The relative yield stress (g) and plastic viscosity (h) increased inversely with the A/P ratio, while the workability increased proportionally. Furthermore, some empirical models are proposed to describe the characteristic of yield stress: plastic viscosity and spread diameter versus the A/P ratio and time with a correlation between the rheological parameters and the spread diameter. The increase in A/P ratio has also followed a decrease in compressive strength in all tested samples for all the ages. As expected, an increase of the porosity accompanied the increase of the A/P ratio.

scholarly journals Effects of Kaolin Addition on Mechanical Properties for Cemented Coal Gangue-Fly Ash Backfill under Uniaxial Loading

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3693
Author(s):  
Faxin Li ◽  
Dawei Yin ◽  
Chun Zhu ◽  
Feng Wang ◽  
Ning Jiang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Fly Ash ◽  
Uniaxial Compressive Strength ◽  
Shear Failure ◽  
Coal Gangue ◽  
Tensile Failure ◽  
Peak Strain ◽  
Local Shear

In this investigation, six groups of cemented coal gangue-fly ash backfill (CGFB) samples with varying amounts of kaolin (0, 10, 20, 30, 40, and 50%) instead of cement are prepared, and their mechanical properties are analyzed using uniaxial compression, acoustic emission, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The uniaxial compressive strength, peak strain, and elastic modulus of CGFB samples decreased with the kaolin content. The average uniaxial compressive strength, elastic modulus, and peak strain of CGFB samples with 10% amount of kaolin are close to that of CGFB samples with no kaolin. The contribution of kaolin hydration to the strength of CGFB sample is lower than that of cement hydration, and the hydration products such as ettringite and calcium-silicate-hydrate gel decrease, thereby reducing strength, which mainly plays a role in filling pores. The contents of kaolin affect the failure characteristics of CGFB samples, which show tensile failure accompanied by local shear failure, and the failure degree increases with the kaolin content. The porosity of the fracture surface shows a decreasing trend as a whole. When the amount of kaolin instead of cement is 10%, the mechanical properties of CGFB samples are slightly different from those of CGFB samples without kaolin, and CGFB can meet the demand of filling strength. The research results provide a theoretical basis for the application of kaolin admixture in fill mining.

scholarly journals Analysis of the Effect of Various Types of Limestone as a Main Constituent of Cement on the Chosen Properties of Cement Pastes and Mortars

2019 ◽  
Vol 65 (3) ◽  
pp. 75-86
Author(s):  
J. Gołaszewski ◽  
G. Cygan ◽  
M. Gołaszewska
Keyword(s):  
Compressive Strength ◽  
Rheological Properties ◽  
Yield Stress ◽  
Drying Shrinkage ◽  
Plastic Viscosity ◽  
Main Constituent ◽  
Cement Pastes ◽  
Mortar Strength ◽  
The Impact

AbstractThe article is an attempt to compare the impact of the use of various types of limestone as the main constituent of cement on selected mortar properties. Four different limestones were added in amount of 15, 30, 40% to CEM I 42.5 R to obtain limestone cemens. Rheological properties (yield stress, plastic viscosity) of fresh mortar, tensile and compressive mortar strength, early shrinkage, and drying shrinkage were tested. Obtained results indicate that both tensile and compressive strength decreases with the increase of the limestone content in cement. Limestone can worsen or improve workability, depending on distribution of limestone grains. The addition of limestone increases the early shrinkage, but reduces the shrinkage after 28 days. Studies show that the granulation of limestone plays an important role in determining the influence of limestone on mortar properties.

scholarly journals Influence of Granite Cutting Waste and Recycled Concrete on Properties of Self Compacting Concrete

2019 ◽  
Vol 8 (4) ◽  
pp. 205-208
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Coarse Aggregate ◽  
Strength Test ◽  
Recycled Concrete ◽  
Fine Aggregate ◽  
Self Compacting Concrete ◽  
Slump Flow ◽  
Hardened Properties ◽  
Passing Ability

This paper explains the combined effect of granite cutting waste and recycled concrete on the workability and mechanical properties of self compacting concrete. Experimental plan is divided in such a way that granite cutting waste is replaced with fine aggregate at 0, 20,40,60,80 and 100% proportions. Recycled concrete is replaced with the coarse aggregate starting from 20 to 100%. Total 36 mixes were designed to check the fresh and hardened properties. Slump flow and T500, v-funnel and L-box test are conducted to know the flow ability and passing ability of concrete. To study the hardened properties compressive strength, flexural strength test values are to be collected.

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