Experiment on the frost resistance of Modified Phospho Gypsum: A case used to Improve Baozhong Railway Subgrade loess

It has been widely recognized that loess has a low stability and permeability,and it is susceptible to a sudden decrease in total volume or collapse upon wetting.When the railway subgrade was under the dynamic trainload,the loess subgrade was prone to instability and liquefaction.loess is higher than that of the cement modified loess,but lower than that of the MPG modified loess.However,the coefficient of permeability for the MPGcement modified loess has an opposite result,and the MPG-cement modified loess specimens have the best frost resistance.In addition,the mechanism of MPG-Bao Zhong railway is a key railway for Guyuan city,in Ningxia province of China,which is an important city of the Belt and Road.Due to the influence of largearea flood irrigation on the farmland,the subgrade had a degree of settlement.The settlement had not been alleviated after three treatments,which seriously affected the safety of the train.For this reason,cement,Modified Phospho Gypsum(MPG)and MPGcement were used to reinforce the subgrade loess,and the unconfined compressive strength test,permeability test and freeze-thaw cycle test were carried out.Then the compressive strength,impermeability and frost resistance of the three were analyzed and compared.The results indicate that the compressive strength of the MPG-cement modified cement modified loess is discussed.It is found that cement and MPG have two hydration reactions with water in loess.Ettringite,the hydration reaction product,which not only fills the pores,restricts the movement of the soil particles,but also acts as a connecting soil particle in the soil particles.Therefore,the strength of the modified loess continues to increase,and the physical properties of the modified loess are improved.

Mechanical and Frost-resistance Properties of Rural Area Building Waste Hollow Bricks

Serving as recycled coarse aggregate,the pretreated rural building waste was added into the concrete hollow bricks in the varying replacement of 0,20%,40%,60%,80% and 100%.By testing its compressive strength,flexural strength,mass and strength loss after freeze-thaw cycles,the impact of the different replacement on mechanical and frost-resistance properties of concrete hollow bricks was presented through SEM analysis.The experimental results show that,with the increase in recycled coarse aggregate replacement rate,the mechanical and frost-resistance properties show a downward trend;when the replacement rate is 40%,28 d compressive strength and flexural strength of concrete hollow brick demonstrate the good peak value which meet the requirement of the national standard for ordinary small concrete hollow bricks;the interfacial structures of the pretreated recycled concrete is more complicated than those of concrete made of natural aggregate,but the former enjoys better interface bonding and tight structure.

Study on Frost Prevention and Drought Resistance Effect of Potato under Different Planting Methods

According to different planting test data,meteorological data,field planting survey and expert interview data in recent years,frost prevention and drought resistance effect of potato under different planting methods were studied using agro-meteorological disaster risk index analysis method. The results showed that the risk index of potato with the full-film planting was small due to good thermal insulation and soil moisture conservation performance. The risk index of potato with half-film planting( flat mulching,ridging planting and furrow planting) was moderate,while that of ridge tillage without mulching,double rows,full of stars and flat planting was large,and their frost prevention and drought resistance effect were poor. It provides support and reference for understanding the frost and drought conditions of potatoes under different planting methods and carrying out insurance weather services for farmers and production managers.

Frost Resistance and Damage Velocity of Compressively Preloaded Concrete

The frost resistance and compressive strength degradation of concrete under the simultaneous action of compressive load and freeze-thaw cycles were experimentally investigated. Air-entrained and non-air-entrained specimens with different water/cement(w/c) ratios were subjected to different compressive stress by specially designed apparatus, while the specimens suffered freeze-thaw cycles. In order to track the strength degradation process, the nondestructive tests were carried out after each freeze-thaw cycle got the residual strength for each specimen. Based on the experimental data, a variable Kss was proposed to describe the damage velocity. Experimental results indicate that the deterioration processes are accelerated by the compressive loads, and the damage velocity increases with the increases of the preloading levels and w/c ratios. The air entrainment decreases the damage velocity and improves the frost resistance of non-air-entrained concrete, although it would reduce the compressive strength of concrete.

Review on frost resistance and anti-clogging of pervious concrete

Pervious concrete is a special type of concrete that is of high porosity and contains no or a small amount of fine aggregate,and it is an important basic material for sponge city construction.The presence of a large number of connected pores inside pervious concrete leads to a marked difference in durability failure mechanism compared with that of ordinary concrete.In this study,the frost resistance and anti-clogging of pervious concrete were introduced in detail,and the methods to improve their performance were summarized systematically.The cracking pattern of pervious concrete is influenced by geometric characteristics and three-dimensional morphological features of pores,resulting in its crack generation,development,and geometry being significantly different from those of ordinary concrete,thus leading to different freeze-thaw cycle mechanisms.In addition,due to its different pore structure compared to ordinary concrete,three types of clogging mechanisms,affecting the long-term permeability of pervious concrete were elaborated systematically(i.e.,physical clogging,biological clogging,and chemical clogging).And the ways to improve the anti-clogging of pervious concrete are systematically presented from multiple perspectives.Finally,in order to broaden the engineering applications of pervious concrete,some research proposals are presented in this study.

The Frost-resisting Durability of High Strength Self-Compacting Pervious Concrete in Deicing Salt Environment

A high strength self-compacting pervious concrete(SCPC) with top-bottom interconnected pores was prepared in this paper. The frost-resisting durability of such SCPC in different deicing salt concentrations(0%, 3%, 5%, 10%, and 20%) was investigated. The mass-loss rate, relative dynamic modulus of elasticity, compressive strength, flexural strength and hydraulic conductivity of SCPC after 300 freeze-thaw cycles were measured to evaluate the frost-resisting durability. In addition, the microstructures of SCPC near the top-bottom interconnected pores after 300 freeze-thaw cycles were observed by SEM. The results show that the high strength SCPC possesses much better frost-resisting durability than traditional pervious concrete(TPC) after 300 freeze-thaw cycles, which can be used in heavy loading roads. The most serious freeze-thaw damage emerges in the SCPC immersed in the 3% of Na Cl solution, while there is no obvious damage in 20% of Na Cl solution. Furthermore, it can be deduced that the high strength SCPC can be used for 100 years in a cold environment.

Frost Resistance of Pervious Concrete Mixed with Waste Glass Powder

The contents of waste glass powder(WGP)(0%,10%,15%,20%,25%)and water-binder ratio(W/C)(0.24,0.26,0.28)were used as influencing factors,and the quality loss rate(Δm)and compressive strength loss rate(Δfc)were used as characterization parameters.The Ca/Si ratio and main element contents of C-S-H gels with different WGP content were investigated by energy dispersive spectrometry(EDS).The pore structure evolution characteristics of WGP composite cementing materials were investigated by low field nuclear magnetic resonance(NMR).UsingΔfc as the index of frost resistance degradation and Weibull function,the frost resistance degradation of glass doped pervious concrete(WGP-PC)was modeled.The results show that,with WGP,for the same number of cycles,Δm andΔfc decrease and increase with the increase of WGP.Under the same WGP content,Δm andΔfc decrease first and then increase with the increase of W/C.After 100 freeze-thaw cycles,the samples with WGP content of 20%and W/C of 0.26 have the best freeze-resistance.Microscopic tests show that with the increase of WGP content,the Ca/Si ratio of C-S-H gel decreases at first and then increases with the increase of WGP content.The extreme value of Ca/Si is 2.36 when WGP is added by 20%.The pore volume of hardened paste with 20%WGP content decreased by 18.6%compared with that of cement system without WGP.The overall compactness of the specimen was improved.On the basis of the test data,a life prediction model was established according to Weibull function.The experiment showed thatΔfc could be used as a durability degradation index,and the slope of the reliability curve became gentle after WGP was added,which reduced the damage degradation rate of PC.W/C was 0.26.It's about 5000 hours.

稻草纤维增强泡沫混凝土物理力学性能试验研究

为了研究稻草纤维增强泡沫混凝土的性能,以普通硅酸盐水泥为主要胶凝材料,硅灰、偏高岭土和粉煤灰为辅助胶凝材料,稻草纤维为增强材料,采用物理发泡法制备纤维增强泡沫混凝土;通过全因子试验,研究在不同水胶比和发泡剂掺量下,稻草纤维掺量对泡沫混凝土的密度、吸水率、抗压强度、抗折强度、劈裂抗拉强度和抗冻性能的影响。结果表明:对于不同水胶比和发泡剂掺量,泡沫混凝土的密度、抗压强度和劈裂抗拉强度均随纤维掺量的增加呈现出先增加后降低的变化规律;抗压强度随密度增加呈幂函数增加关系;劈裂抗拉强度随抗压强度的增加呈指数函数增加关系;当水胶比为0.45时,抗折强度随纤维掺量的增加先增加后降低,当水胶比为0.50时,抗折强度随纤维掺量的增加而增加;纤维的掺入增大了泡沫混凝土的泡孔尺寸和吸水率,降低了其抗冻性能。

混凝土冻融作用下冻结应力演化规律及对抗冻性能的影响

为了探究严寒地区混凝土冻害机理及冻结应力对混凝土抗冻性的影响,基于大型极端气候模拟器模拟-40℃低温冻害的条件,采用研制的冻结应力测试装置对F300高抗冻等级混凝土在冻融单次降温阶段及降温-升温冻融循环两种模式下的冻结应力及抗冻性能进行研究,同时利用了环境扫描电子显微镜对冻融循环作用下的混凝土微观裂缝进行了测试研究。研究表明:-40℃单次降温过程中降温速率越快,冻结应力出现的时间越早、混凝土内部产生的冻结应力增幅也越大;冻融循环降温阶段产生的冻结应力会随降温-升温冻融作用的不断循环而累积增大,且冻结应力的发展存在转变拐点,在相同降温终了试件中心低温条件下,降温阶段的降温速率越大,冻结应力由增加转入减小的拐点出现越早;冻融过程中的冻结应力与混凝土质量损失、相对动弹性模量两个抗冻性常用评价指标有较好的对应关系;冻结应力逐步使水泥浆体产生损伤,表现为微观裂缝的生成与发展,损伤积聚产生冻害。

含引气剂海工混凝土的抗冻性能及其梁受弯承载力

为了研究引气剂对海工混凝土抗冻性能及其梁受弯承载力的影响,对2种配合比6根海工混凝土梁及相应的冻损试件进行总计100次快速冻融试验;采用质量损失率、动弹性模量损伤度和抗压强度损失率对混凝土冻融损伤程度进行有效评价;考虑混凝土抗压强度退化以及等效矩形应力图系数的变化,提出了冻融作用下海工混凝土梁正截面受弯承载力计算公式。结果表明:加入引气剂可以增强海工混凝土的抗冻性能,降低梁的开裂弯矩退化速率,但会降低混凝土强度和梁的极限弯矩;在150次冻融循环内,提出的模型能够较好地预测冻融作用下海工混凝土梁的正截面受弯承载力。

纤维-地聚物混凝土力学性能及耐久性能研究

为改善地聚物混凝土的力学性能和耐久性,通过掺入不同长度和掺量的聚丙烯纤维,对地聚物混凝土的力学性能、抗冻性、抗氯离子侵蚀性及抗裂性进行了研究,并基于SEM试验,从微观角度进一步解释聚丙烯纤维的作用机理.结果表明:聚丙烯纤维的掺入能够提高地聚物混凝土的力学性能和耐久性能,当纤维掺量为0%~0.6%时,随着纤维掺量的增加,地聚物混凝土的改善效果越明显.当掺量超过0.6%时,其力学性能和耐久性开始下降.通过SEM分析也表明,聚丙烯纤维能够提高基体内部的整体性和密实性,从而显著改善地聚物混凝土的力学性能和耐久性.最终推荐掺量0.6%长度为12 mm的聚丙烯纤维为最佳掺量.

冻融循环下水工混凝土的相对动弹性模量和质量变化规律研究

为了研究冻融循环条件下水工混凝土相对动弹性模量和质量的变化规律,基于混凝土冻融破坏机理和现实情况分析,通过预制混凝土护坡砌块和不同配合比水工混凝土试件的快速冻融试验,分析了质量损失率、相对动弹性模量和冻融循环次数的关系。结果表明:冻融试件质量损失率转为正值时为相对动弹性模量快速降低之时,此时混凝土的含水率为快速破坏含水率;冻融过程中,试件质量前期增加,后期减少,但相对动弹性模量一直降低;可以通过快速修补、防渗处理等方式延缓水工混凝土达到快速破坏含水率,实现提高抗冻性能的目的。

聚丙烯纤维橡胶混凝土的力学及抗冻性能研究

研究了聚丙烯纤维的体积掺量(0.45%、0.90%、1.35%、1.80%、2.25%、3.41%、4.51%)对橡胶混凝土力学及抗冻性能的影响,并建立了冻融损伤劣化模型来预测橡胶混凝土的冻融损伤劣化规律。结果表明:掺入适量聚丙烯纤维可以有效提高橡胶混凝土的力学及抗冻性能,当聚丙烯纤维掺量在1.80%~2.25%范围内时,试件的力学及抗冻性能均较好;建立的冻融损伤劣化模型的拟合系数R2均大于0.992,拟合精度较高,可为聚丙烯纤维橡胶混凝土在寒冷地区工程中的应用提供理论依据。

双芯微胶囊法自修复混凝土冻融试验研究

寒区水工混凝土长时间遭受冻融破坏和水流冲刷会形成联合破坏,修复难度较大、成本高、效果不理想,最终影响工程安全运行,而微胶囊自修复技术可实现混凝土自我修复。通过以E51型环氧树脂为内芯材,以固化剂PETMA为外芯材,以尿素和甲醛制备的脲醛树脂为壁材,采用原位聚合法制备出双芯微胶囊,研究结果表明:双芯微胶囊呈球状,粒径分布在40μm左右,表面饱满圆润,芯材含量为24.3%,包覆率为48.6%,热稳定性较好;混凝土在掺入双芯微胶囊后,在受到冻融破坏时能及时破裂,并释放出修复剂和固化剂对混凝土进行修复,混凝土抗冻等级也有效提高,最大可提高38.5%;双芯微胶囊掺量阈值为3%,掺量超过阈值后,修复效果会减弱。

小果甜柿遗传转化体系建立及其抗冻性遗传改良的初步研究

【目的】建立小果甜柿(Diospyros kaki Thunb.‘Xiaoguo Tianshi’)叶片再生和优化其遗传转化体系,以期通过分子育种技术获得抗冻性强的砧木新种质。【方法】以小果甜柿叶盘为外植体,首先通过不同生长素(IAA)质量浓度和细胞分裂素(ZT,TDZ)配比探讨对其愈伤诱导和不定芽再生的影响;进而探讨其叶片对不同抗生素质量浓度组合的敏感性;此外,利用根癌农杆菌介导的叶盘稳定遗传转化体系,进一步探讨超表达君迁子(D.lotus L.)抗寒基因DlCBF1对小果甜柿叶盘再生植株抗冻性的影响。【结果】叶圆片在MS(1/2N)+ZT 2.0 mg·L^(-1)+TDZ 2.0 mg·L^(-1)培养基中愈伤形成率最高(64.71%);将愈伤组织接种到MS(1/2N)+ZT 2.0 mg·L^(-1)+IAA 0.1mg·L^(-1)生芽培养基中,不定芽再生率和不定芽数分别为31.11%和2.37个。头孢霉素质量浓度为400 mg·L^(-1)时可抑制农杆菌生长,且叶片愈伤形成率低(9.84%);卡那霉素对叶片再生影响大,在质量浓度为20 mg·L^(-1)时其愈伤诱导率为11.57%。小果甜柿叶片稳定超表达君迁子DlCBF1基因,获得再生植株73株,其中阳性植株5株,荧光定量结果分析,阳性植株#1和#47中DlCBF1基因表达量分别为野生型的13倍和11倍。经过-4℃低温处理8 h后,超表达株系与野生型株系相比,叶片受伤害程度更小,光合作用效率变化不明显,电导率低,H_(2)O_(2)和O_(2)^(-)在组织中的积累少,阳性株系表现出比野生型株系更强的抗冻性。【结论】在优化小果甜柿叶片外植体再生和稳定遗传转化体系的基础上,通过在小果甜柿叶片中超表达君迁子DlCBF1基因,获得6.85%转基因阳性再生植株,稳定超表达DlCBF1基因可显著增强小果甜柿再生植株的抗冻性。研究结果为培育抗冻性强的柿砧木新种质提供了科学依据。

矿物掺合料对再生混凝土抗冻性与可再生性的影响

为探究矿物掺合料对再生混凝土抗冻性与可再生性的影响,本文选取硅灰、粉煤灰和粒化高炉矿渣三种矿物掺和料,通过不同掺量组合制备了五组不同胶凝体系的再生混凝土。采用快冻法对再生混凝土进行冻融试验,通过测定冻融过程中再生混凝土的相对动弹性模量、质量损失率和抗压强度损失率评价其抗冻性,采用SEM观察冻融后再生混凝土的微观结构。此外,对冻融后的再生混凝土进行破碎,获得二代再生粗骨料,并依据其表观密度、压碎值、坚固值和吸水率评估再生混凝土的可再生性。结果表明:5%(质量分数,下同)硅灰+20%粉煤灰+20%矿渣+55%水泥组合的质量损失率和抗压强度损失率明显比单掺5%硅灰以及5%硅灰+20%粉煤灰和5%硅灰+20%矿渣组合的低,且相对动弹性模量比其他组合的高。四种不同胶凝体系的二代再生粗骨料物理性能均达Ⅲ类标准,可用于强度等级为C25的结构混凝土的制备。

基于陶粒纤维混凝土的衬砌渠道抗冻胀性能研究

为改善北方寒区预制混凝土衬砌渠道存在衬砌板件自重大、尺寸小、装配效率低等问题,探讨将陶粒纤维混凝土用于衬砌渠道。基于正交试验法开展9组陶粒纤维混凝土和1组C35普通混凝土冻融前后力学性能试验,并结合冻胀数值模拟分析衬砌渠道抗冻胀性能变化。结果表明:陶粒纤维混凝土抗压强度因素影响次序为页岩陶粒体积取代率>聚丙烯纤维(PP)掺量>陶粒预湿时间,抗拉强度因素影响次序为PP掺量>页岩陶粒体积取代率>陶粒预湿时间,冻融后陶粒纤维混凝土抗压、抗拉强度损失率低于普通混凝土;衬砌渠道数值模拟的抗冻胀性能变化与材料性能变化趋势一致,陶粒纤维混凝土衬砌渠道抗冻胀性能损失小于普通混凝土衬砌渠道,最优抗冻胀性能损失减小4.68%,同时衬砌板重量减小18.47%;陶粒纤维混凝土作为渠道衬砌材料具有明显质轻的装配化优势。

MU10再生混凝土承重砌块力学性能与抗冻性试验研究

为进一步提高废弃混凝土利用率,促进严寒地区应用再生混凝土承重砌块,在分析再生骨料物理性能的基础上,考虑了100%再生粗骨料取代率、水胶比、用水量及粉煤灰掺量的影响,采用正交试验设计了C30再生混凝土配合比来制备MU10再生混凝土承重砌块,通过分析MU10再生混凝土承重砌块的力学性能,确定了MU10再生混凝土承重砌块的最佳配合比,利用环境模拟箱验证了MU10再生混凝土承重砌块的抗冻性。结果表明:再生骨料与天然骨料相比表面较粗糙,附着部分旧水泥砂浆,具有低密度,高孔隙率、吸水率和含泥量,压碎指标是天然骨料的两倍左右;MU10再生混凝土承重砌块的最佳配合比为再生粗骨料1 172 kg/m^(3)、天然河砂578 kg/m^(3)、水泥400 kg/m^(3)、粉煤灰100 kg/m^(3)、水150 kg/m^(3),其抗压强度为11.4 MPa,抗折强度为2.1 MPa,可用于承重及有抗震要求的砌体结构;经过50次冻融循环后,MU10再生混凝土承重砌块的质量损失为1.2%、强度损失为18.1%,抗冻性能符合要求,可以作为严寒地区新型墙体材料使用。

抗冻型人造土冻融适应性及其在边坡植被修复中的应用

[目的]探究抗冻型人造土冻融适应性及其在高寒地区边坡植被修复中的实践效果,为高寒地区边坡植被修复工程应用提供理论依据和应用支撑。[方法]采用室内冻融循环试验剖判人造土在冻融循环60次期间的理化性质变化特征,结合主成分分析确定室外试验监测指标的选取,现场取样监测了近4 a人造土在西藏高寒地区岩质边坡的工程应用及其植被修复效果,并与当地天然土作对照分析。[结果]与天然土相比,抗冻型人造土的抗冻稳定性和肥力均有显著提升(p<0.05),具体表现在其冻融前后的相对动弹性模量、>0.25 mm水稳性大团聚体含量、平均重量直径(MWD)、团聚度及有机质、铵态氮、硝态氮、速效磷和速效钾含量显著提升,而质量损失率和结构破坏率显著降低(p<0.05)。主成分分析显示,室内试验指标中的相对动弹性模量、结构破坏率、pH值和有机质含量与主成分因子的相关性较高,因此在室外试验中监测这4个指标和植被修复情况。室外监测中发现抗冻型人造土4 a内在不同时间段上的结构破坏率均更低,相对动弹性模量和有机质含量更高;其边坡植被修复后的植被覆盖率、物种多样性、地上和地下生物量均更佳。[结论]抗冻型人造土在高寒地区应用时的植被修复效果更佳,特别是其抗冻耐久性、团聚体稳定性和肥力表现突出,均优于天然土,因此其更适宜于边坡植被修复应用。

粉煤灰对渠道用混凝土抗冻及抗冲磨性能的影响

新疆北疆地区混凝土渠道冻胀及冲刷磨损严重,渠道用混凝土成本偏高,为合理利用新疆地区粉煤灰资源,保证装配式渠道用混凝土抗冻及抗冲磨性能,本文制备了粉煤灰掺量分别为胶凝材料的0%(质量分数,下同)、10%、20%、30%的混凝土,同时结合装配式混凝土渠道企业生产用配合比,对混凝土进行力学性能、冻融循环、冲刷磨损试验。结果表明:混凝土3、7 d的力学性能随粉煤灰掺量的增加而降低,粉煤灰掺量为10%的混凝土28 d力学性能最优,达57.8 MPa;混凝土抗冻性能随粉煤灰掺量的增加呈先增大后减小的趋势,粉煤灰掺量为20%的混凝土抗冻性能最佳,与未掺粉煤灰的混凝土相比,粉煤灰掺量为10%、20%的混凝土抗冻性能均有所提升;混凝土抗冲磨性能随粉煤灰掺量增大呈先上升后下降趋势,粉煤灰掺量为10%的混凝土抗冲磨性能最好,与未掺粉煤灰的混凝土相比,其抗冲磨性能提升了约12%,表明粉煤灰对混凝土抗冻及抗冲磨性能有较明显的改善作用。