聚丙烯纤维对硅灰混凝土氯离子渗透性能的影响

在正交试验的基础上,采用NEL试验方法研究了不同掺量(体积掺量0.067%～0.5%)、不同尺度(3、6、10 mm)的聚丙烯纤维混杂对硅灰混凝土抗氯离子渗透性能的影响.研究表明,聚丙烯纤维影响硅灰混凝土抗氯离子渗透性能的因素依次为:长短纤维掺量比＞纤维掺量＞复合纤维长度.当纤维掺量在低掺量范围内增加时,硅灰混凝土氯离子渗透性能会降低,而当纤维掺量较高时,硅灰混凝土氯离子渗透性能反而增加;纤维对硅灰混凝土氯离子渗透性能的影响与复合纤维的长度关系不大,而与长短纤维掺量比关系密切.     

Effect of silica fume and steel fibers on some properties of high-strength concrete

The main disadvantage of high-strength concrete is its highly brittle behavior and this can beovercome by adding fibers to the concrete. This would also improve some other mechanical properties of high-strength concrete such as tensile strength and compressive strength. These properties are not very well established for high-strength steel-fiber reinforced concrete (HSFRC) yet. In this study the influence of silica fume on the properties of HSFRC were investigated by using silica fume of two different percentages and three different hooked-end fibers namely, 30/0.50, 60/0.80 and 50/0.60 length/diameter (mm/mm). Fibers were added to concrete in three different volume percentages of 0.5, 1.0 and 2.0 by volume of concrete. The results indicated that there is a linear function between splitting tensile strength (F_splt) and volume percentage of fibers (V_f) [i.e. F_plt = A(V_f) + B, where A and B are correlation coefficients] as well as between splitting tensile strength (F_splt) and compressive strength (F_c) of plain series A concrete [i.e. F_splt = C (√F_c) + D, where C and D are correlation coefficients]. These relations can describe the development of splitting tensile strength of HSFRC containing no silica fume, 5% silica fume and 10% silica fume by weight of cement. On the other hand, although silica fume has an effect on compressive strength, volume percentage and aspect ratio of steel fibers has little effect.     

The effects of polypropylene fibers on the properties of reinforced concrete structures

In this study, the results of polypropylene fibers reinforced concrete properties have been presented. The compressive strength, permeability and electric resistivity of concrete samples were studied. The concrete samples were made with different fibers amounts from 0 to 2 kg m⁻³. Also, the samples fabricated with coral aggregate and siliceous aggregate were examined and compared. The samples with added polypropylene fibers of 1.5 kg m⁻³ showed better results in comparison with the others. Moreover, coral aggregate concrete showed less electric resistivity and less compressive strength in comparison with samples fabricated of siliceous aggregates. It is concluded that the coral aggregates are not suitable for making concrete or using in concrete structures in the onshore atmosphere.     

Properties of polypropylene fiber reinforced silica fume expansive-cement concrete

This paper reports on a comprehensive study on the mechanical properties of expansive-cement concrete containing silica fume and polypropylene fibers. Properties studied include those of the fresh mix properties, length change, rapid chloride permeability, compressive strength, flexural behavior, and bond of hardened concrete. Silica fume content used was 5 and 10% and fiber volume fraction was 0.10, 0.30, and 0.50%. Results show that the use of 5% silica fume combined with 0.30% fiber volume fraction results in optimum mixture design for repair applications from the standpoints of workability, bond, strength, length change and permeability.     

硅粉混凝土的基本性能与工程应用

硅粉混凝土具有良好物理力学性能和耐久性能,为了进一步提高硅粉混凝土的应用效率,分析总结了硅粉混凝土的试验研究和工程应用成果,指出了硅粉在混凝土中的作用机理以及硅粉混凝土的应用技术要点.     

新型增密硅灰对混凝土性能影响的研究

研究了掺加新型增密硅灰混凝土性能与掺加原状硅灰混凝土性能,实验结果表明,该新型增密硅灰有效地减小了混凝土的坍落度损失率、凝结时间,泌水率。混凝土的抗压强度、劈裂强度、抗硫酸盐腐蚀、抗渗性均与原状硅灰混凝土性能相近。新型增密硅灰降低运输成本,具有良好的经济和社会效益。     

硅粉对混凝土高温后力学性能影响的试验研究

用硅粉替代部分水泥掺入混凝土中,对混凝土试块进行200～ 800℃的高温处理,再对冷却后的混凝土试块进行质量损失率测定、超声波检测、抗压强度试验、劈裂抗拉强度试验和微观试验,并对试验结果进行分析和拟合.结果 表明:硅粉会增加混凝土的抗压强度、脆性以及高温爆裂几率,减小高温后混凝土的质量损失率,其最佳掺量为8％,在600...     

Effect of elevated temperature on the mechanical properties of concrete produced with finely ground pumice and silica fume

This study investigated the effect of elevated temperature on the mechanical and physical properties of concrete specimens obtained by substituting cement with finely ground pumice (FGP) at proportions of 5%, 10%, 15% and 20% by weight. To determine the effect of silica fume (SF) additive on the mechanical and physical properties of concrete containing FGP, SF has been added to all series except for the control specimen, which contained 10% cement by weight instead. The specimens were heated in an electric furnace up to 400, 600 and 800 °C and kept at these temperatures for one hour. After the specimens were cooled in the furnace, ultrasonic pulse velocity (UPV), compressive strength and weight loss values were determined. The results demonstrated that adding the mineral admixtures to concrete decreased both unit weight and compressive strength. Additionally, elevating the temperature above 600 °C affected the compressive strength such that the weight loss of concrete was more pronounced for concrete mixtures containing both FGP and SF. These results were also supported by scanning electron microscope (SEM) studies.     

聚丙烯纤维和硅粉对再生混凝土的强化试验研究

再生混凝土由于再生骨料自身的缺陷：富含杂质、孔隙率高、吸水性大、强度低等，限制了其应用范围。通过试验研究，得出利用聚丙烯纤维和硅粉对再生混凝土进行强化．可以明显改善其力学性能．提高其强度；研究了聚丙烯纤维和硅粉掺量对再生混凝土强度的影响，为实际工程应用，提供了理论依据。     

The effect of silica fume and high-volume Class C fly ash on mechanical properties,chloride penetration and freeze–thaw resistance of self-compacting concrete

In this study, cement has been replaced with a Class C fly ash (FA) in various proportions from 30% to 60%. Durability properties of various self-compacting concrete (SCC) mixtures such as, freezing and thawing, and chloride penetration resistance have been investigated besides mechanical properties within the scope of this study. Similar tests were carried out with the incorporation of 10% silica fume (SF) to the same mixtures. Test results indicate that SCC could be obtained with a high-volume FA. Ten percent SF additions to the system positively affected both the fresh and hardened properties of high-performance high-volume FA SCC. Although there is a little cement content, these mixtures have good mechanical properties, freeze–thaw and chloride penetration resistance.     

Deep learning model for estimating the mechanical properties of concrete containing silica fume exposed to high temperatures

In this study, the deep learning models for estimating the mechanical properties of concrete containing silica fume subjected to high temperatures were devised. Silica fume was used at concentrations of 0%, 5%, 10%, and 20%. Cube specimens (100 mm × 100 mm × 100 mm) were prepared for testing the compressive strength and ultrasonic pulse velocity. They were cured at 20°C±2°C in a standard cure for 7, 28, and 90 d. After curing, they were subjected to temperatures of 20°C, 200°C, 400°C, 600°C, and 800°C. Two well-known deep learning approaches, i.e., stacked autoencoders and long short-term memory (LSTM) networks, were used for forecasting the compressive strength and ultrasonic pulse velocity of concrete containing silica fume subjected to high temperatures. The forecasting experiments were carried out using MATLAB deep learning and neural network tools, respectively. Various statistical measures were used to validate the prediction performances of both the approaches. This study found that the LSTM network achieved better results than the stacked autoencoders. In addition, this study found that deep learning, which has a very good prediction ability with little experimental data, was a convenient method for civil engineering.     

Mechanical properties and impact resistance of concrete composites with hybrid steel fibers

The aim of this study is to develop concrete composites that are resistant to armor-piercing projectiles for defense structures. Different reinforcement configurations have been tested, such as short steel fibers, long steel fibers, and steel mesh reinforcement. Three different concrete mix designs were prepared as “Ultra High Performance (UHPFRC), High Performance (HPFRC) and Conventional (CFRC) Fiber Reinforced Concrete”. The content of hybrid steel fibers was approximately 5% in the UHPFRC and HPFRC mixtures, while the steel fiber content was approximately 2.5% in the CFRC mixture. In addition, a plain state of each mixture was produced. Mechanical properties of concrete were determined in experimental studies. In addition to the fracture energy and impact strength, two important indicators of ballistic performance of concrete are examined, which are the penetration depth and damage area. The results of the study show that the depth of penetration in UHPFRC was around 35% less than that in HPFRC. It was determined that the mixtures of UHPFRC and HPFRC containing 5% by volume of hybrid steel fibers showed superior performance (smaller crater diameter and the less projectile penetration depth) against armor-piercing projectiles in ballistic tests and could be used in defense structures.     

Acidic resistance of materials based on the novel use of silica fume in concrete

The objectives of this paper are the results of a study on the acidic resistance of cement-based materials prepared with chemically modified silica fume (MSF). MSF seems to be a highly effective hardening accelerator of materials based on combinations of Portland cement and basic blast furnace slag and on this slag alone. Besides the mechanical properties chemical resistance is a very important engineering property of concretes. This is very interesting even with cement-based materials with a MSF application. It was a reason for the study on the acidic resistance of the cement-based materials when MSF was applied. Based on the observation of changes of chemical composition, pore structure and mechanical properties of the test specimens, a high acidic resistance was found on the cement-based materials when MSF was applied. This allowed a solution to the problem of insufficient acidic resistance of current cement-based materials which represents a crucial world-wide problem.     

关于硅灰和高性能混凝土的一些思考

硅灰的商业化应用在美国已有25年的历史。在此期间,硅灰从一种处于研究阶段的材料演变成一种在混凝土中被广泛规定使用的组分。硅粉在被市场所接纳的时间,恰好是“高性能混凝土”一词产生的前夕,有充分的理由说明：最初的硅灰混凝土项目正是高性能混凝土的起源。本文简述了在美国市场中硅灰使用的发展历史;回顾了硅灰混凝土如何发展成为高性能混凝土;并总结了使用硅灰的适用场合、配合比、抹面和施工性能等方面的经验。     

硅粉在混凝土中的应用探讨

作者分析了硅粉在混凝土中的作用机理，以及硅粉对混凝土物理、力学性能的影响，从而指出在混凝土中掺入适量的硅粉，是一种所需投资较少且有明显效果的方法，并可带来良好的环境效益和社会效益。     

The effect of polypropylene fibers on the properties of fresh and hardened lightweight self-compacting concrete

This paper evaluates the LECA Lightweight Self-Compacting Concrete (LLSCC) manufactured by Nan-Su, of which the Packing Factor (PF) of its design mixing method has been modified and improved.The study analyzes the impact of polypropylene fibers on LLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition.The evaluation of Fiber Reinforced LLSCC (FR-LLSCC) fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete.For the mechanical properties of LLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic modulus and flexural strength, all of which were measured after the sample being cured for 28 days.When self-compacting concretes were lightened to 75% of their normal weight, their fresh properties are affected immensely.Applying 0.3% volume fractions of polypropylene fiber to the LLSCC resulted in 40% reduction in the slump flow (from 720 mm to 430 mm). In general, the rate of slump flow over Super Plasticizer (SP) volume percentage reduced with the use of polypropylene fibers in the FR-LLSC.Polypropylene fibers did not influence the compressive strength and elastic modulus of LLSCC, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength.     

复掺粉煤灰和硅灰对混凝土抗氯离子渗透性和抗冻性的影响研究

通过试验研究了复掺粉煤灰和硅灰对混凝土抗氯离子渗透性能和抗冻融性能以及综合考虑两个方面对混凝土耐久性的影响.试验结果表明:复掺粉煤灰和硅灰能大幅度提高混凝土的抗氯离子渗透性能,最小能提高51.3％,同时会降低其抗冻融性能,但降低幅度不是很大,相对动弹模最大仅降低12.5％,因此综合评价其对耐久性的影响,复掺粉煤灰和硅灰...     

钢渣粉硅灰混凝土的力学性能及耐久性研究

通过试验测试分析了钢渣粉单掺以及与硅灰二元复掺混凝土在不同配合比下的和易性、力学性能和耐久性能,并基于改性前后混凝土微观结构特征的测试分析揭示了钢渣粉单掺以及与硅灰二元复掺对混凝土材料的改性机理。试验研究结果表明:钢渣粉取代混凝土中水泥最适宜的比例是10%,此时混凝土的力学性能和耐久性能都得到有效的提高,掺量20%的钢渣混凝土与普通硅酸盐混凝土各项性能相近。钢渣粉与硅灰的二元复掺可以使混凝土的力学性能和耐久性得到显著提高。钢渣粉在混凝土中的作用有两个:一是作为活性胶凝材料发生水化反应,但其活性比水泥低;二是微集料效应,分散水泥颗粒填充混凝土的孔隙,提高混凝土的密实度。     

无硅灰C80高性能混凝土研究

本文在混凝土理论配合比的基础上，仅改变各掺合料的比例及总掺合料与水泥的比例关系，采用混凝土用中砂配制砂浆，探索了一条以砂浆流动性指导高强高性能混凝土配制的新方法，并应用该方法以290kg/m^3，42．5R普通硅酸盐水泥及粉煤灰、矿渣粉和沸石粉等矿物掺合料配制出28d强度为96MPa的无硅高性能混凝土。