Synthesis and Flocculation of Polyacrylamide with Low Water Absorption for Non-dispersible Underwater Concrete

The polyacrylamide which is directly added into concrete shows strong water absorption property.Thus the construction of underwater constructure would demand high amount of water,resulting in poor workability of concrete and strength shrinkage after hardening.Herein,a kind of anionic polyacrylamide(APAM)grafted with water reducing functional group(-COOH)was synthesized at low temperatures by partial factor design and response surface design.The structure and morphology of APAM were characterized by UV,FTIR and SEM methods.The experimental results show that the molecular weight of the synthesized APAM could reach 11 million,under the condition that the temperature was 35℃,the pH value was 8,the monomer concentration was 27wt%,the initiator dosage was 0.6wt%,and the monomer ratio(n(AM):n(AA))was 3.When the APAM was applied into the underwater slurry,it presented good flocculation and low water demand.When the dosage was 1%of the mass of the cement,the water demand increased by 12%,which could meet the self-leveling and anti-dispersity of the underwater slurry at the same time.This technology provides technical guidance for the large-scale industrial production of polyacrylamide for underwater concrete construction while achieving environmental protection during production.

Analysis on Pore Structure of Non-Dispersible Underwater Concrete in Saline Soil Area

In this paper,mercury intrusion porosimetry(MIP)is used to test the pore structure of non-dispersible underwater concrete so as to study the influence of pouring and curing environment,age and slag powder on the pore characteristics of concrete,analyze the pore characteristics,porosity and pore distribution of concrete in different hydration stages,and reveal the relationship between pore structure and permeability of concrete.The results show that the pore-size distribution of concrete in fresh water condition is better than that in sulfate environment and mixed salt environment,and therefore,sulfate as well as mixed salt are not conducive to the development of pore structure of non-dispersible underwater concrete;chlorine salt has little effect on the pore structure of nondispersible underwater concrete;under the three conditions of sulfate,chlorine and mixed salt,the porosity of concrete mixed with slag powder is lower than that of concrete without slag powder.The results indicate that the addition of slag powder can ameliorate the pore size distribution of non-dispersed underwater concrete,reduce the porosity,and make the concrete structure more compact,which is beneficial to improve the permeability resistance of concrete at the macro level.

Effect of GGBS on performance deterioration of non-dispersible underwater concrete in saline soil

In saline soil areas,there are a large number of ions in soil or water environments,such as Cl^(-)and SO_(4)^(2-),which have strong corrosive interactions with buildings.To study the deterioration of non-dispersible underwater concrete in sulfate,chloride,and mixed salt environments,the compressive strength and deterioration resistance coefficient of the studied concrete mixed with different amounts of ground granulated blast-furnace slag(GGBS)were analyzed in this paper.At the same time,the micro morphology and corrosion products distribution of the studied concrete were observed by means of SEM,plus XRD diffraction,TG-DTG and FT-IR analyses to explore the influence of corrosive solutions on the hydration products of concrete.We also analyzed the mechanism of improving the deterioration resistance of the studied concrete by adding GGBS in a saline soil environment.The results show that the compressive strength of the studied concrete in a chloride environment was close to that in a fresh water environment,which means that chloride has no adverse effect on compressive strength.The deterioration of the studied concrete was most serious in a sulfate environment,followed by mixed salt environment,and the lowest in a chloride environment.In addition,by adding GGBS,the compressive strength and deterioration resistance of the studied concrete could be effectively improved.

Study of damage to a high concrete dam subjected to underwater shock waves

To study the effect of a strong underwater shock wave on a concrete dam, this research aims to improve hammer impact methods in model tests. Six 1:200 scale models were designed and tested under distributed impact loads. A device was deployed for a direct measurement of the impact force at the upstream face of the dams. The model dam bases were anchored to prevent displacement. The experimental results indicate that the top part of the concrete dam is a weak zone, and the impact failure initiates with a fracture on the top of the dam. The peak value of impact stress increases when the second crack appears in the concrete dam from the upstream face to the downstream face. And, the level of the second crack in the dam body is lower as the peak value of impact stress increases. In this study, dynamic analysis was conducted by calculating the results to verify the effectiveness of a device to directly measure the impact force. This method may be used to approximately forecast the damage of concrete dam and may also be useful in other engineering applications.

Preparation of High Performance Non-dispersible Concrete

A new-type underwater non-dispersible concrete admixture NDA was prepared,its function mechanism was analyzed,and C40 high performance non-dispersible underwater concrete was manufactured by applying NDA.The results indicate that NDA has a suitable workability,low strength loss,and excellent anti-dispersion;the fresh non-dispersible underwater concrete with NDA has high anti-dispersion,excellent workability such as self-compacting and not bleeding;hardened non-dispersible underwater concrete with NDA has a high strength,high durability such as high anti-abrasion,impermeability and anticorrosion.

The damage to model concrete gravity dams subjected to water explosions

Over the past century,the safety of dams has gradually attracted attention from all parties.Research on the dynamic response and damage evolution of dams under extreme loads is the basis of dam safety issues.In recent decades,scholars have studied the responses of dams under earthquake loads,but there is still much room for improvement in experimental and theoretical research on small probability loads such as explosions.In this paper,a 50-m-high concrete gravity dam is used as a prototype dam,and a water explosion model test of a 2.5-m-high concrete gravity dam is designed.The water pressure and the acceleration response of the dam body in the test are analysed.The pressure characteristics and dynamic response of the dam body are assessed.Taking the dam damage test as an example,a numerical model of concrete gravity dam damage is established,and the damage evolution of the dam body is analysed.By combining experiments and numerical simulations,the damage characteristics of the dam body under the action of different charge water explosions are clarified.The integrity of the dam body is well maintained under the action of a small-quantity water explosion,and the dynamic response of the dam body is mainly caused by the shock wave.Both the shock wave and the bubble pulsation cause the dam body to accelerate,and the peak acceleration of the dam body under the action of the bubble pulsation is only one percent of the peak acceleration of the dam body under the action of the shock wave.When subjected to explosions in large quantities of water,the dam body is seriously damaged.Under the action of a shock wave,the dam body produces a secondary acceleration response,which is generated by an internal interaction after the dam body is damaged.The damage evolution process of the dam body under the action of a large-scale water explosion is analysed,and it is found that the shock wave pressure of the water explosion causes local damage to the dam body facing the explosion.After the peak value of the shock wave,the impulse continues to act on the dam body,causing cumulative damage and damage inside the dam body.

Numerical study on local failures of reinforced concrete slabs against underwater close-in explosions

Reinforced concrete(RC)slabs are the primary load-carrying member of underwater facilities.They can suffer severe local failures such as cratering,spalling,or breaching as a result of underwater close-in(UWCI)explosions.In this study,we established a fully validated high-fidelity finite element analysis approach to precisely reproduce the local failures of RC slabs after a UWCI explosion.A recently proposed dynamic constitutive model is used to describe wet concrete.The effects of free water content on the material properties,including the tensile/compressive strength,elastic modulus,strain rate effect,failure strength surface,and equation of state,are comprehensively calibrated based on existing test data.The calibrated material parameters are then verified by a single-element test.A high-fidelity finite element analysis(FEA)approach of an RC slab subjected to a UWCI explosion is established using an arbitrary Lagrangian-Eulerian(ALE)algorithm.Simulating previous UWCI explosion tests on RC orifice targets and underwater contact explosion tests on saturated concrete slabs showed that the established FEA approach could accurately reproduce the pressure-time history in water and damage patterns,including the cracking,cratering,and spalling,of the RC orifice target and saturated concrete slab.Furthermore,parametric studies conducted by simulating an RC slab subjected to a UWCI explosion showed that:(i)the local failure of an RC slab enlarges with increased charge weight,reduced standoff distance,and reduced structural thickness;(ii)compared to a water-backed RC slab,an air-backed RC slab exhibits much more obvious local and structural failure.Lastly,to aid the anti-explosion design of relevant underwater facilities,based on over 90 simulation cases empirical formulae are summarized to predict local failure modes,i.e.,no spall,spall,and breach,of water-and air-backed RC slabs subjected to a UWCI explosion.

Experimental investigation on dynamic response and damage models of circular RC columns subjected to underwater explosions

Reinforced concrete(RC) columns are widely used as supporting structures for high-piled wharfs.The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharfs antiknock security.In this study,the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models.Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m,under different explosive quantities(0.025 kg-1.6 kg),stand-off distances(0.0 m-7.0 m),and detonation depths(0.25 m-2.0 m).The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure,acceleration,strain,and displacement.Then,the load distribution characteristics,time history of test data,and damage models related to present conditions were obtained and discussed.Three damage models,including bending failure,bending-shear failure and punching failure,were identified.In addition,the experie nce model of shock wave loads on the surface of a RC column was proposed for engineering application.

Influence of Hydrostatic Pressure on Compressive Strength of Self-consolidating Concrete

The design of unique chamber, in which the SCUWC （self-consolidating underwater concrete） can be tested under the impact of the hydrostatic pressure from 0.1 MPa to 0.5 MPa, is presented in the paper. The results of the preliminary tests of the effect of the hydrostatic pressure on the compressive strength of SCUWC were shown. The impact of the hydrostatic pressure on the compressive strength values of test specimens has been confirmed. There has been an increase in the strength of the specimens taken from the upper parts of the concrete samples. As it can be seen from the preliminary research, the differences in compressive strength are related to the differences that occur in the size and distribution of air voids in the samples taken from upper and lower parts of the test specimens. On the basis of the carried out investigations of the compressive strength, it can be concluded that the hydrostatic pressure has a favorable effect on the compressive strength of the tested specimens of SCUWC. Increase of the compressive strength is observed mostly in the upper layers of the samples. Preliminary analysis of the quantity and distribution of air pores in the samples of concrete subjected to pressure 0.5 MPa confirms the positive impact of the hydrostatic pressure on the layers close to the surface indicated by the absence of large air voids above 1,500μm and by reducing the quantity of air pores of size above 300μm.

水下自护混凝土与钢筋握裹力试验研究

随着水下自护混凝土技术的推广和应用,其关键工艺参数水下保护剂浓度对水下自护钢筋混凝土结构性能的影响成为关注的热点。基于水下自护技术,在常用工作浓度范围内,对水下自护混凝土的素混凝土力学性能、混凝土与钢筋握裹力、微观孔隙结构开展了试验研究。试验结果表明:在不同水下保护剂浓度下,水下自护素混凝土抗压强度水陆强度比均超过80%;混凝土与钢筋握裹力水陆强度比约在40%~65%,水下保护剂浓度越高,混凝土与钢筋握裹力水陆强度比越低;混凝土基质区域孔隙率和混凝土与钢筋握裹力存在负相关关系;水下保护剂能够有效提升水下自护混凝土的力学性能,但水下保护剂浓度的提升会对混凝土与钢筋握裹力强度造成不利影响。因此,合理选择水下保护剂浓度并增加钢筋用量是提升水下自护钢筋混凝土工程的可靠性的重要举措。

远场水下爆炸冲击作用下重力坝动力稳定性的简化时程分析方法

高坝大库的抗爆与防护是国防安全的重要研究课题。该文针对远场水下爆炸冲击作用下混凝土重力坝的稳定安全评价问题,研究了远场水下爆炸冲击波的传播及其与坝体的相互作用过程;基于波动理论和平面波假设,建立了重力坝爆炸动应力场的简化理论计算模型,最终建议了一种远场水下爆炸冲击波作用下重力坝动力稳定性的简化时程分析方法;同时结合工程实际,采用该方法对某混凝土重力坝的动力稳定性进行了分析。结果表明:在远场爆炸冲击荷载作用下,重力坝的稳定安全系数呈现出先增后减再增并最终保持恒定的变化规律;下游坝面反射形成的拉伸波与剪切波的共同作用是导致建基面稳定安全系数降低的主要原因。

钢筋混凝土拱的水下抗爆性能

为探究水下爆炸荷载作用下钢筋混凝土拱的动力响应特性和破坏特征,制作了两个钢筋混凝土拱试件,并开展了水下爆炸试验。试验分为拱外爆炸和拱内爆炸两组,采用10 g乳化炸药,试验时爆源距结构面最小距离为10 cm(起爆点位于拱结构正上方和正下方),通过传感器记录爆炸试验中钢筋混凝土拱典型断面处的水压力及加速度时程曲线。基于Arbitrary Lagrange-Euler(ALE)算法,建立了空气-水-炸药-钢筋混凝土拱等多介质动态耦合作用模型,将数值模拟结果与试验结果对比,验证了数值方法的可靠性。采用验证后的数值模型进一步研究了拱外及拱内爆炸荷载作用下钢筋混凝土拱的动力响应差异。结果表明:相同炸药当量下,内部爆炸有更多的能量作用于混凝土拱,使结构的动力响应更强烈;外部爆炸下,拱顶、拱腰处产生较大裂缝;内部爆炸时,迎爆面裂缝数量明显增多,拱肩位置出现裂缝。钢筋混凝土拱形结构抵抗外部爆炸荷载的能力明显强于内部爆炸荷载。

水下修复材料的黏结强度与变形性能研究进展

介绍了常用的几种水下修复材料的性能,分析了其作用机理,强调了黏结强度和变形性能的重要性,指出了各水下修复材料在接缝修复中存在的问题及优缺点,并提出了未来重点研究方向。

水下不分散混凝土抗分散剂优化设计与凝结时间调控

水下不分散混凝土(non-dispersible underwater concrete,NDC)为涉水工程的施工提供抗冲刷能力,为实现水下不分散混凝土性能的提升,文章探讨抗分散剂的优化设计和凝结时间的调控,选取聚丙烯酰胺(polyacrylamide,PAM)和羟丙基甲基纤维素(hydroxypropyl methyl cellulose,HPMC)作为抗分散剂主剂,聚羧酸减水剂、有机硅和聚醚类消泡剂作为辅剂,从抗分散性和流动性的角度对水下不分散混凝土抗分散剂的组成进行优化设计,同时选取碳酸锂和硫酸铝作为调凝剂,对水下不分散混凝土的凝剂时间进行调控。研究结果表明:采用HPMC作为主剂、聚羧酸减水剂和聚醚类消泡剂作为辅剂制备抗分散剂,可以使得水下不分散混凝土具有较好的抗分散性和流动性;其中,含水泥质量分数0.45%的HPMC和1%聚羧酸减水剂的新拌水泥砂浆(水胶质量比为0.5,胶砂质量比为2)表现出优异的抗分散性和良好的流动性,其pH值为9,扩展度为150 mm;在该体系中,硫酸铝的调凝效果较好且经济效益更高,但使用时用量应少于2%。对抗分散剂的优化设计和凝结时间的调控为水下不分散混凝土的相关实验研究提供了重要参考。

重力式码头沉箱水下修复技术

对已建码头的加固改造,实现码头质量安全水平的有效提升,可推动基础设施的集约利用。本文以海南某已服役多年的3.5万吨级散货码头项目为例,对主体沉箱结构破损的加固实践研究,提出水下修复的解决方案。研究结果表明:1)通过水下摄像及探摸,可准确判断沉箱损坏情况;2)对于沉箱壁碎裂、钢筋裸露锈蚀严重或断裂的现象,可先采用高压水冲洗或凿槽切除处理,然后支立模板与浇筑高强灌浆料,并采用水下包覆层材料对沉箱壁进行修补;3)对于沉箱内填料部分掉落的现象,可在沉箱仓格内整体浇筑水下不分散混凝土。经现场试验检测,该施工修复技术满足设计要求,且归纳总结了相应的质量控制要点及水下作业安全管理要求,旨在为类似工程提供参考。

水下机器人在入海水道通榆河立交工程涵洞的探查应用

入海水道通榆河立交工程经多年运行,需对难以精确检查的水下部分进行详实探查。结合历年水下检查成果报告、工程现状调查分析报告等资料,以20#涵洞为典型场景,选择搭载水下光学摄像设备、二维图像声呐传感器、全向成像声呐等设备的水下机器人进行水下探查,为工程运行管理和安全评估提供参考。

水下不分散混凝土的配制及性能影响

采用单一变量法和正交试验法,探究了水胶比、絮凝剂掺量和粉煤灰掺量对水下不分散混凝土流动性、抗压强度及抗渗性能的影响。结果表明:絮凝剂掺量对混凝土流动性影响最大,为保证施工时混凝土有较好的流动性,絮凝剂掺量不宜过多,采用粉煤灰适量取代水泥,能节约经济成本,提高混凝土的流动性。水胶比对混凝土抗压强度和抗渗性能的影响最大,当水胶比为0.39、絮凝剂掺量为3.0%、粉煤灰掺量为15%时,水下不分散混凝土的抗压强度与抗渗性能最高。

接触爆炸下波纹钢⁃混凝土板复合结构水下防爆效果评价

为探究不同波纹钢⁃混凝土板复合结构的水下抗爆防护效果,采用有限元⁃光滑粒子流体动力学耦合算法(FEM⁃SPH)建立水下多介质耦合爆炸模型;设计不同波纹钢⁃混凝土板复合结构防护方案,探究不同复合结构防护层(含3,6,9,12 mm厚波纹钢复合结构、含30°,45°,60°,75°波纹钢复合结构和含10,30,50,70 mm波高波纹钢复合结构)的水下削波吸能效果,并提出耗能分担率对复合结构进行防护效果评价。研究结果表明:混凝土板迎爆面与背爆面的模拟结果与试验结果较为吻合,验证了水下接触爆炸模拟过程;不同复合结构防护方案下,含12 mm厚波纹钢复合结构、含75°波纹钢复合结构和含70 mm波高波纹钢复合结构防护方案较无防护方案测点峰值压力最大降幅为63.2%,60%和57.9%,最大防护率分别为63.2%,60.0%和57.9%,耗能分担率为69.48%,66.26%和63.51%;最优型式(厚度为12 mm/夹角为75°/波高为70 mm)复合结构的削波吸能效果及防护效果均显著优于单一因素影响下的复合结构。研究成果可为不同波纹钢⁃混凝土板复合结构在水下抗爆防护领域的应用提供理论基础。

大掺量粉煤灰制备水下不分散混凝土及性能研究

因为特殊的施工环境,需要动态平衡水下不分散混凝土的新拌流动性能和抗分散性能。研究了大掺量粉煤灰对混凝土工作性能、抗分散性和力学性能的影响。结果表明,粉煤灰掺量不大于50%时,可以实现大掺量粉煤灰水下不分散混凝土的制备。综合考虑材料性能和经济性能,粉煤灰掺量为50%时水下不分散混凝土性能较优,此时新拌混凝土坍落度、扩展度分别为250、545 mm;屈服应力、塑性黏度分别为47.4 Pa、4.4402 Pa·s;抗分散性能良好;7、28 d抗压强度及水陆强度均达到一等品要求。

过河段顶管施工渗水冒顶水下混凝土全包封处置方法

为解决过河段机械顶管施工渗水冒顶问题,采用分幅围堰施工形成相对干燥场地,对管网上下游采用气囊封堵防止水流继续流入,人工对原有管道进行修复,最后进行水下混凝土全包封施工。该方法工艺成熟可靠,操作简单,施工风险低,对周边环境影响小,可以很好地解决过河段管道渗漏水影响施工进展问题。为冒顶事故的进一步处理创造良好的施工条件。