偏高岭土地聚物力学性能研究进展

偏高岭土是高岭土在适当温度下煅烧活化形成的硅铝酸盐,以其为原料制备的地聚物具有快硬早强、强度高、和易性好及耐腐蚀等优点。近年来,相关学者针对偏高岭土地聚物力学性能的影响因素开展了大量力学性能试验及基础理论研究工作,为偏高岭土地聚物的推广应用奠定了基础。综述了偏高岭土地聚物的种类、水化机理,总结了激发剂种类、掺量、水玻璃模数、胶凝材料处理方式、液固比、外掺料及养护方式、养护温度等因素对偏高岭土地聚物力学性能的影响,并对偏高岭土地聚物推广应用中面临的问题及未来的研究方向进行了探讨。     

Preparation and characterisation of fly ash based geopolymer mortars

Geopolymer mortars with varying levels of sand aggregate were prepared and their physical and mechanical properties studied. The geopolymer binder to sand aggregate weight ratio was varied from 9 to 1. Compressive strength and Young’s modulus of the fly ash based geopolymer paste were 60 MPa and 2.27 GPa and these values did not change significantly with addition of up to 50 wt.% sand aggregate. Geopolymer binder exhibited strong bonding to the sand aggregate. Increasing sand content without increasing the amount of alkaline activator resulted in a decreasing level of geopolymerisation within the binder system.     

Composition,strength and workability of alkali-activated metakaolin based mortars

This study has investigated the joint effect of several factors on the workability and mechanical strength of alkali-activated metakaolin based mortars. The factors analysed through a laboratory experiment of 432 specimens, pertaining to 48 different mortar mixes were, sodium hydroxide concentration (10 M, 12 M, 14 M, 16 M), the superplasticizer content (1%, 2%, 3%) and the percentage substitution of metakaolin by calcium hydroxide in the mixture (5%, 10%). The results show that the workability decreases with the concentration of sodium hydroxide and increases with the amount of calcium hydroxide and superplasticizer. The results also show that the use of 3% of superplasticizer, combined with a calcium hydroxide content of 10%, allows improving the mortar flow from less than 50% to over 90%, while maintaining a high compressive and flexural strength.     

偏高岭土地质聚合物仿瓷材料的试验研究

以偏高岭土为原料,水玻璃为激发剂制备了地质聚合物材料,研究了激发剂的模数、掺量、水土比及养护方式对地质聚合物抗压强度的影响,确定了此类地质聚合物的最佳制备条件为水玻璃模数1.0,碱掺量10%,水土比0.25,自然条件下养护,并探讨了地质聚合物的开裂和气泡问题,从而制备了性能优良的地质聚合物仿瓷材料。     

Performance evaluation of cement mortars modified with metakaolin or ground brick

The work analyzes the performance of mortars prepared with two metakaolin samples and ground calcined-clay brick. Complete stress–strain deformation response under compression, porosity, sorptivity, pore size distribution and resistance to penetration of chloride ions have been determined for mortars with up to 40% cement replacement. Continuum damage mechanics analyzes using a scalar model allowed to extract information on the mode of deformation leading to failure of the mortars during compressive loading. It is shown that not only the ultimate strength, but also the pre-peak deformation response is influenced by calcined-clay addition. The ultimate strength of the mortar mixture depended on the type of calcined-clay added, but in all cases mortars with addition were marginally more compliant during the elastic deformation stage and more brittle as fracture approached.     

Seismic retrofitting of severely damaged RC connections made with recycled concrete using CFRP sheets

An experimental and numerical program is carried out in this research to investigate the influence of CFRP sheets on the cyclic behavior of unconfined connections made with recycled concrete. Cement is partially replaced by silica fume, iron filling and pulverised fuel ash using two different percentages: 15% and 20%. Each specimen is partially loaded at the first stage and then specimens are repaired using CFRP sheets. The repaired specimens are then laterally loaded until failure. In addition, a finite element model is built in ABAQUS and verified using the experimental results. The experimental results have shown that the repaired specimens have regained almost double the capacity of the un-repaired specimens and hence the adopted repair configuration is recommended for retrofitting seismically vulnerable RC connections. Increasing cement replacement percentage by silica fume, fuel ash or iron filling from 15% to 20% has reduced joint carrying capacity and weakened the joint. It is recommended using 15% pulverised fuel ash or silica fume as cement partial replacement to enhance the strength and ultimate drift of beam-column joints under cyclic loading. Iron filling concrete is also recommended but the enhancement is relatively less than that found with pulverised fuel ash concrete and silica fume concrete.     

Resistance to acid degradation,sorptivity, and setting time of geopolymer mortars

Experimental evaluations were conducted to determine the water sorptivity, setting time, and resistance to a highly acidic environment, of mortar with alkali-activated ground granulated blast furnace slag (GBS) binder and also of combinations of fly ash and GBS binders. Binders were activated using mixtures of NaOH and Na₂SiO₃ solutions. The molarity of NaOH in the mixtures ranged from 10 mol·L⁻¹ to 16 mol·L⁻¹, and the Na₂SiO₃/NaOH ratio was varied from 1.5 to 2.5. Mortar samples were produced using three binder combinations: 1) GBS as the only binder; 2) blended binder with a slag-to-fly ash ratio of 3:1; and 3) mixed binder with 1:1 ratio of slag to fly ash. Mortar samples were mixed and cured at (22 ± 2) °C till the day of the test. The impact of activator solution alkalinity, activator ratio Na₂SiO₃/NaOH, GBS content on the rate of water absorption were evaluated. After 7, 28, and 90 d of immersion in a 10% sulfuric acid solution, the resistance of a geopolymer matrix to degradation was assessed by measuring the change in sample weight. The influence of solution alkalinity and relative fly ash content on setting times was investigated. Alkali-activated mortar with a slag-to-fly ash ratio of 3:1 had the least sorptivity compared to the two other binder combinations, at each curing age, and for mortars made with each of the NaOH alkaline activator concentrations. Mortar sorptivity decreased with age and sodium hydroxide concentrations, suggesting the production of geopolymerization products. No reduction in weight of sample occurred after immersion in the strong acid H₂SO₄ solution for three months, regardless of binder combination. This was due to the synthesis of hydration and geopolymerization products in the presence of curing water, which outweighed the degradation of the geopolymer matrix caused by sulfuric acid.     

Performance of alternative CFRP retrofitting schemes used in infilled RC frames

A number of experimental studies have been reported in recent literature about the beneficial effects of infill walls on the seismic response of reinforced concrete (RC) frames. The experimental study presented in this paper mainly focuses on the behavior of bare and carbon fiber reinforced polymer (CFPR)-retrofitted infilled RC frames with different bracing configurations. Quasi-static experimental results are presented and discussed on six 1/3-scaled infilled RC frames that were retrofitted using CFRP material in various schemes. The test results showed a significant increase in the yield and ultimate strength capacities of the frames with a decrease in relative story drifts, especially in the cross-braced and the cross diamond-braced type of retrofitting schemes. The energy dissipation capacities of the retrofitted frames turned out to be more than those of the bare infilled frame, thus reducing the seismic demand imposed on the frames. The cross diamond-braced type of retrofitting scheme, which was positioned on the infill wall and outside the beam–column connection regions of RC frame, showed the best behavior among the other schemes. This scheme not only prevented brittle shear failures of the infill wall, but also prevented the transfer of additional forces to the weak and brittle beam–column connections.     

碳纤维布(板)在加固混凝土结构中的应用

以混凝土结构旧楼加固工程为例,介绍了碳纤维布的性能,以及在加固工程中采用的具体构造做法和施工工艺。采用碳纤维加固的工程没有出现任何质量问题,施工效果良好。     

碳纤维布约束混凝土的受力性能分析

本文就碳纤维 (CFRP)约束混凝土柱的受力性能进行了试验研究 ,通过分析柱截面形状 (圆形、方形 )、CFRP加固量等不同因素对约束混凝土性能的影响 ,提出了便于工程应用的经验算式。依据本文的算式 ,其计算结果和试验结果基本吻合     

预应力混凝土空心板加固工程实例分析

采用在板面叠合钢筋混凝土层并结合板底粘贴碳纤维布方法加固预应力混凝土空心板,根据现行规范对这种加固方法进行分析讨论.     

碳纤维增强塑料布与混凝土基层粘结行为研究

通过自行设计的试验方法,研究了30组粘贴有碳纤维增强塑料布(CFRP布)的混凝土试件粘结界面的破坏形态、粘结应力和碳纤维增强塑料布应变分布特性以及粘结破坏的发展过程.结果表明,粘结应力由碳纤维增强塑料布的加载端向自由端逐渐传递,破坏瞬时发生,破坏形式以剥离破坏为主;存在一个有效粘结长度,约为100 mm.研究结果说明自行设计的粘结试验方法有一定可行性,可为测定CFRP布-混凝土界面粘结强度指标提供新的思路.     

Experimental investigation of mortars using activated Hwangtoh

Hwangtoh (loess) is a Korean traditional building material that is environment-friendly. It is a natural pozzolanic material with many advantages as a substitute for cement-based materials. It has a high heat-storing capability along with purifying, deodorizing and antibiotic properties. Moreover, the emission of infrared radiation from Hwangtoh is beneficial to the human body. However, because of several practical disadvantages, such as shrinkage cracking and low strength development of concrete incorporating Hwangtoh, the application of Hwangtoh as a mineral admixture has not been quite successful. This study attempts to utilize the advantages of Hwangtoh in the field of modern construction, and suggests potential application of Hwangtoh as a substitute for cement-based material. For this purpose, Hwangtoh is activated in the furnace to investigate the optimal activation conditions and the physical properties of mortar incorporating Hwangtoh are investigated. It is found from the results that Hwangtoh shows changes in phase composition and the least amount of voids when activated in the range of 800–850 °C. The slump flow decreases as fineness and replacement ratio increases. The mortar incorporating Hwangtoh still has problems in flow behavior and drying shrinkage, but, at least, our findings lead us to conclude that the activated Hwangtoh can be used as pozzolanic mineral admixtures.     

预应力碳纤维布加固混凝土梁施工

研制了对碳纤维布施加预应力的锚具及施工机具 ,通过试验研究、工程实际应用形成了施工工艺。试验表明用预应力碳纤维布加固梁 ,能充分利用碳纤维布强度 ,改善了梁的结构性能 ,加固效果显著提高。     

碳纤维加固混凝土梁的有限元分析

文章运用有限元分析软件ANSYS建立了CFRP抗弯加固梁的有限元分析模型,通过与试验结果对比,有限元计算结果与试验结果吻合较好,表明文章中建立的CFRP抗弯加固梁有限元模型较为合理。利用该模型,可对CFRP抗弯加固梁进行更深入的研究,也可用于实际加固工程的辅助分析与设计。     

极地低温下CFRP筋与混凝土的黏结性能

开展了碳纤维增强聚合物(CFRP)筋-混凝土试件的拉拔试验,考虑混凝土强度、CFRP筋直径、黏结长度、保护层厚度等参数,分析了极地低温对CFRP筋与混凝土黏结性能的影响规律.结果 表明:与常温相比,极地低温降低了CFRP筋与混凝土的黏结性能,但在18～-80℃范围内,随着温度的降低,其黏结强度并非呈现单一趋势的变化规律;随着CFRP筋直径和黏结长度的增加,CFRP筋与混凝土的黏结强度呈降低趋势,提高混凝土强度或增大保护层厚度将提高其黏结强度;极地低温条件下CFRP筋与混凝土的黏结界面趋于脆性,易发生突然且随机的界面破坏,而不易发生混凝土的劈裂破坏.     

Properties of polymer-modified mortars using epoxy and acrylic emulsions

Water based polymer systems are often used for improvement in the properties of plain cement mortar or concrete. Presently, latexes of a single or combinations of polymers like polyvinyl acetate, copolymers of vinyl acetate–ethylene, styrene–butadiene, styrene–acrylic, and acrylic and styrene butadiene rubber emulsions are generally used. One of the limitations of these polymer systems is that they may re-emulsify in humid alkaline conditions. To overcome this problem, an epoxy emulsion based polymer system has been developed. In this paper the properties of the cement mortar modified with this newly developed epoxy emulsion are compared with those of the acrylic-modified mortar. The results showed that the mortars with the newly developed system have superior strength properties and better resistance to the penetration of chloride ions and carbon dioxide.     

CFRP加固混凝土板的承载力分析

在钢筋混凝土板的加固工程中,有些板只能在正弯矩区加固,而无法在板端负弯矩区加固.本文针对这种情况,利用双向板的设计理论-塑性铰线法,研究了碳纤维复合材料(CFRP)加固混凝土板的设计方法,并推导了加固设计的理论计算公式.并利用理论公式和有限元软件ANSYS计算板的承载能力,计算结果表明,在板底局部粘贴CFRP能显著提高板的承载能力,因而是一种有效的加固方法.     

CFRP加固混凝土板的承载力分析

在钢筋混凝土板的加固工程中,有些板只能在正弯矩区加固,而无法在板端负弯矩区加固.针对这种情况,利用双向板的设计理论-塑性铰线法,研究了碳纤维复合材料(CFRP)加固混凝土板的设计方法,并推导了加固设计的理论计算公式.并利用理论公式和有限元软件ANSYS计算板的承载能力,计算结果表明,在板底局部粘贴CFRP能显著提高板的承载能力,因而是-种有效的加固方法.