高温对纤维增韧高性能混凝土残余力学性能影响的试验研究

本文通过测定钢纤维、聚丙烯纤维和混杂纤维(聚丙烯纤维和钢纤维)增韧高性能混凝土的高温残余强爱和断裂能，研究聚丙烯纤维、钢纤维和混杂纤维对混凝土高温残余力学性能的影响。实验结果表明，钢纤维和混杂纤维，尤其是钢纤维，显著提高高性能混凝土的残余强度和断裂能。聚丙烯纤维对高性能混凝土残余力学性能的影响很小。     

Concrete cover effect on reinforced concrete bars exposed to high temperatures

The mechanical properties of structural reinforcement steel have been investigated after the exposure to high temperatures. Plain steel, reinforcing steel bars embedded into mortar and plain mortar specimens were prepared and exposed to 20, 100, 200, 300, 500, 800 and 950 °C temperature for 3 h individually. The S420 deformed steel bars with diameters of ∅10, ∅16 and ∅20 were used. The mortar was prepared with CEM I 42.5 N cement and fly ash. The tension tests on reinforcements taken from cooled specimens were performed, and the variations in yield strength, ultimate strength and in resilience of three different dimensioned reinforcements were determined. A cover of 25 mm provides protection against high temperatures up to 400 °C. The high temperature exposed plain steel and the steel with 25-mm cover has the same characteristics when the reinforcing steel is exposed to a temperature 250 °C above the exposure temperature of plain steel.     

Experimental study of mechanical properties of normal-strength concrete exposed to high temperatures at an early age

In China, accidental fires are known to occur during construction, causing concrete to be exposed to high temperatures when it is at an early age (i.e. “young”). In this paper, compressive and splitting tensile strengths of concretes cured for different periods and exposed to high temperatures were obtained. The effects of the duration of curing, maximum temperature and the type of cooling on the strengths of concrete were investigated. Experimental results indicate that after exposure to high temperatures up to 800 °C, early-age concrete that has been cured for a certain period can regain 80% of the compressive strength of the control sample of concrete. The 3-day-cured early-age concrete was observed to recover the most strength. The type of cooling also affects the level of recovery of compressive and splitting tensile strength. For early-age concrete, the relative recovered strengths of specimens cooled by sprayed water are higher than those of specimens cooled in air when exposed to temperatures below 800 °C, while the changes for 28-day concrete are the converse. When the maximum temperature exceeds 800 °C, the relative strength values of all specimens cooled by water spray are lower than those of specimens cooled in air.     

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.     

The effect of high temperatures on the mechanical properties of concrete made with different types of aggregates

The main objective of this paper was to assess the benefits of using materials that were formed at high temperatures as an aggregate for concrete that was exposed to high temperature. The fire resistance of concrete made with some locally available, potential “fire-resistant” aggregates, such as diabase, steel slag, crushed bricks and crushed tiles, was investigated. The specimens of measurements 4×4×16 cm³ were kept in molds for 24 h and, after demolding, were kept in water at room temperature of about 20±2 °C until testing. At the age of 28 days, the specimens, with moisture content within the limits of 3-5%, were exposed to high temperatures in a previously heated test furnace. The residual mechanical properties (compressive and flexural strengths) of these concretes after natural cooling were compared with the residual mechanical properties of concrete made with commonly used river and dolomite aggregates. The replacement of natural concrete aggregates with brick and steel industry waste materials was justified, not only in terms of increased fire resistance, but also in terms of more responsible waste disposal.     

早龄期混凝土高温性能试验研究

针对目前施工工地频繁发生火灾,如何处理现场上经历火灾后的混凝土构件的问题,提出了研究早龄期混凝土高温性能的思路。对强度等级为C30的早龄期混凝土进行了高温试验,探讨了受高温时的龄期、高温目标温度和冷却方式对试件经历高温后可恢复的残余强度的影响。研究发现：这3个因素对早龄期混凝土高温后残余抗压强度影响较大。养护龄期3d时的混凝土试件高温后可恢复的残余强度最大;龄期为7～28d的混凝土经受高温后,在两种冷却条件下,随着所经受的高温温度增大,其可恢复的残余强度变化趋势类似;小于28d龄期的试件喷水冷却后,其可恢复的残余强度比自然冷却的明显提高,与28d龄期混凝土受热后残余强度的规律相反。     

超高性能混凝土高温后残余力学性能试验研究

测定了抗压强度高于140MPa的含粗骨料超高性能混凝土和活性粉末混凝土遭受高温作用后的残余抗压强度、残余劈裂抗拉强度和残余断裂能。结果显示,两种超高性能混凝土的残余强度均随着目标温度的升高而呈现先增大再降低的趋势,而残余断裂能均随着目标温度的升高逐渐降低。各目标温度下,含粗骨料超高性能混凝土的残余抗压强度均高于活性粉末混凝土,但其残余劈裂抗拉强度和断裂能低于后者。活性粉末混凝土在300℃临界温度下的峰值残余抗压强度和峰值残余劈裂抗拉强度分别比常温时提高了26.8%和19.3%,800℃高温后的强度损失率分别为72.3%和81.4%。含粗骨料超高性能混凝土在400℃临界温度下的峰值残余抗压强度和在300℃目标温度下的峰值劈裂抗拉强度分别比常温时提高了34.0%和6.8%,800℃高温后的强度损失率分别为70.2%和84.9%。所以,对于有抗火灾高温要求的工程结构,含粗骨料超高性能混凝土适合用于受压构件,而活性粉末混凝土适宜于抗弯构件。     

碳纤维混杂纤维混凝土高温后力学性能试验研究

通过高温电阻炉持续加热掺入碳纤维与碳纤维混杂纤维的混凝土,分析了在不同温度加热后,各种纤维混凝土物理力学性能的变化情况,通过设置温度变量,定量分析了不同温度下混杂纤维混凝土的变化与损伤规律,试验结果表明混杂纤维提高了混凝土的安全性。     

不同龄期混凝土高温后力学性能研究

为研究不同龄期混凝土高温后的力学性能变化,对不同养护龄期的混凝土设置不同的温度和继续养护时间,对其抗压强度和劈裂抗拉强度进行试验.结果表明:各龄期混凝土的抗压强度和劈裂抗拉强度随经历温度的升高基本呈下降趋势,但当温度不高于100℃,龄期不大于14 d时,其强度反而略有上升.混凝土经历相同温度情况下,高温时龄期越早,强度...     

关于混凝土最小水泥用量的讨论

本文着重讨论相关规范标准对混凝土最小水泥用量的要求，并对现时仍然存在的一些对“水泥”这一概念的认识误区进行分析。     

重载高抗折强度水泥混凝土的配制及其力学性能研究

本文通过室内试验，研究了使用高效减水剂和粉煤灰、粒化高炉矿渣、沸石粉配制重载作用下高抗折强度水泥混凝土的方法，并分析了不同类型高抗折强度水泥混凝土的力学特性。     

Research on mechanical behavior of recycled aggregate concrete after high temperatures

以历经最高温度、再生粗骨料取代率、粗骨料类型、混凝土强度为变化参数,设计和制作了168个再生混凝土标准棱柱体试件,对其进行高温后的物理及力学性能试验。试验中观察了高温后试件的表观变化及其受力破坏形态,获取了再生混凝土的高温烧失率以及各试件的轴心受压全过程应力-应变曲线,通过分析各变化参数对历经高温后再生混凝土的物理及力学性能的影响规律,根据最高受火温度和质量烧失率分别提出高温后再生混凝土轴心抗压强度评估公式。结果表明：随着温度的提高,高温后再生混凝土由青灰色变为棕灰色,最后呈灰白色,出现温度裂缝及剥落现象;烧失率随着温度的提高、取代率的增大和强度的降低而显著增大;温度对高温后再生混凝土破坏形态及力学性能的影响最大,温度越高,其轴心受压破坏时的裂缝带越宽,破坏程度越严重;随着温度的升高,其弹性模量的衰减程度要比峰值应力的大;相比卵石骨料再生混凝土,高温对碎石骨料再生混凝土力学性能的影响更为显著;混凝土强度和再生粗骨料取代率变化对高温后再生混凝土的力学性能无明显影响。基于试验结果提出的高温后再生混凝土轴心抗压强度的评估计算结果与实测结果吻合较好。     

The effect of alkali reactivity on the mechanical properties of concrete

The effects of highly reactive aggregate, fused silica, and slowly reactive aggregate, Thames Valley sand, on the mechanical properties of concrete were investigated in this paper. The mechanical properties studied over a period of 12 months were the compressive strength, direct tensile strength, tensile splitting strength, flexural tensile strength (modulus of rupture), static modulus of elasticity and water absorption. The effects of both reactive aggregates on the mechanical properties of concrete were compared with that of sound concrete mix. The results presented in this investigation show that the effect of the reactive aggregates on the mechanical properties varies, depending on the type of reactive aggregate. From this study it appears that the direct tensile and static modulus of elasticity were the best indicators of reactivity.     

高温对高炉矿渣混凝土力学性能的影响试验研究

为了研究高温对含有高炉矿渣的混凝土的性能的影响,采用其占比分别为水泥质量的0,10％、30％、50％时,所制备混凝土试件在150~700 ℃下的高温试验,测定了混凝土的质量损失、碳化深度、残余抗压强度和弹性模量。结果表明,随温度升高,混凝土试样的质量损失和碳化深度逐渐增加,且矿渣掺杂量越多,质量损失和碳化程度越大。此外,混凝土试样的抗压强度和弹性模量随温度升高而降低,10%矿渣掺量的混凝土试样的相对抗压强度值最高,高掺量矿渣的相对弹性模量低于低掺量的混凝土试样。     

高性能混凝土的抗火灾高温研究进展

本文对目前高性能混凝土的抗火灾高温性能的研究进展进行了总结。高性能混凝土具有良好的力学性能及耐久性能,然而在火灾高温中极易发生破坏成为高性能混凝土广泛应用的绊脚石。通过在混凝土中掺加聚丙烯纤维、钢纤维等提高高性能混凝土的抗火灾高温性能成为学者们研究的热门领域。掺加聚丙烯纤维是防止高性能混凝土发生高温爆裂的有效措施,掺加钢纤维的高性能混凝土可以保持较高的残余力学性能,混掺纤维（钢纤维和聚丙烯纤维）是提高高性能混凝土抗火灾高温性能的良好途径。在高性能混凝土中掺加橡胶粉、引气剂等其他组分是研究高性能混凝土抗火灾高温性能的新思路。     

再生高强混凝土基本力学性能研究

为研究再生粗骨料取代率与玄武岩纤维对再生高强混凝土的抗压强度、抗折强度、劈裂强度与弹性模量的影响,对再生高强混凝土78个试件进行试验。试验结果表明,相同强度等级下,随再生粗骨料取代率增加,混凝土坍落度、抗压强度和弹性模量存在下降趋势;随着玄武岩纤维含量的增大,混凝土抗折强度与劈裂强度呈现先增加后下降的趋势,但对混凝土抗压强度影响较小。当再生粗骨料取代率取30%时,混凝土强度高且和易性好,为适宜的取代率。     

钢纤维高强混凝土的力学性能研究

通过掺入体积含量０ ．６ ％ ～１．８ ％ 的短切钢纤维,与Ｃ６０ ～Ｃ８０ 高强混凝土复合,制作钢纤维高强混凝土。研究了钢纤维高强混凝土的抗压、劈拉和抗弯强度以及抗弯韧性指数等参数的规律。探讨了钢纤维高强混凝土的强度复合机理和力学特性。     

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...     

Masonry exposed to high temperatures: Mechanical behaviour and properties—An overview

The paper summarises the available information about the behaviour of masonry assemblies and components exposed to high temperatures and fire. A general frame is provided by fire resistance issues in current code provisions and observations from real events, theoretical as well as experimental researches on materials' performance during and after exposure to high temperatures. In particular, the newly acquired engineering approach to fire design has raised the need for improvements in the knowledge of fire and post-fire behaviour of structures at a material scale; thus, the paper particularly focuses on the mechanical properties of masonry materials, that are still scarcely investigated, especially in the residual (i.e. post-fire) situation. Detailed comments are given about the temperature-dependence of the relevant mechanical properties for masonry and its components, that are put into comparison. Then, the main research needs are outlined in the conclusions.