微生物矿化沉积碳酸钙技术修复混凝土既有微裂缝研究进展

混凝土由于具有容易成型、价格低廉、抗压强度高等特点而被广泛应用。但由于混凝土具有各向异性特性,其在服役期间往往不可避免出现裂缝,导致混凝土结构出现渗水,严重时导致结构失效。为延长既有混凝土在实际工程应用中的服役寿命,近年来,研究人员探索利用一种微生物诱导碳酸钙沉积(Microbial-induced carbonate precipitation, MICP)技术进行既有混凝土微裂缝的修复。该技术绿色环保,生物碳酸钙与混凝土基体相容性好,而且修复液粘性低,易进入裂缝空间,修复物质在裂缝内分布更均匀,成为当下的研究热点。MICP技术在混凝土中的应用与碳酸钙矿化沉积机制和修复工艺存在密切关系。本文拟从微生物矿化诱导碳酸钙沉积机制、修复工艺两个方面总结微生物矿化沉积碳酸钙技术在混凝土既有微裂缝修复的研究进展。微生物矿化机制中脲酶催化作用沉积碳酸钙机制由于时间短、碳酸钙产量高,在许多领域中被广泛研究,但是副产物氨不容忽视,对此提出多种矿化机制相结合的方法。修复剂各组分的添加建议采取一步法或两步法中的“细菌、尿素+钙源”组合。而添加工艺方面,相比于浸泡法和喷洒法,注射法对混凝土既有裂缝修复适用性...     

供氧剂浓度和浸泡位置对MICP再生骨料性能的影响

优化矿化方式是提高微生物矿化沉积(MICP)修复再生骨料效果的有效途径.本研究通过改变供氧剂浓度和再生骨料在培养液中的浸泡位置,分析不同矿化方式对再生骨料物理性能的影响,并通过微观分析进一步验证试验结果.结果表明:当过氧化钙浓度为15 g/L,浸泡位置为培养液中部时,MICP再生骨料吸水率降幅为40.4％,压碎指标降幅为19.7％,孔隙率显著降低且孔径分布最佳,同时产生大量碳酸钙晶体填充骨料裂缝,矿化沉积效果最优.     

MICP在建筑领域中的应用进展

城镇化的快速推进带动了我国建筑行业的蓬勃发展,绿色建筑与可持续性发展成为人们关注的热点.一方面,基于生物碳酸钙具有的胶凝特性,利用微生物诱导碳酸钙沉积(MICP)技术可以胶结和加固砂土颗粒.与拌合法相比,喷洒法使固结砂土表现出更高的硬度和抗压强度;采用压力灌浆和循环灌浆的方式能进一步降低固结砂土的渗透系数和吸水率,提高其无侧限抗压强度和干密度.另一方面,基于菌液与胶结液粘度低、颗粒粒径小的特点,MICP技术可修复混凝土微裂纹、强化再生骨料,且修复后的混凝土和强化后的再生骨料表现出更为优异的物理力学性能.MICP是微生物通过自身代谢活动产生的CO32-与周围环境中的Ca2+结合生成生物碳酸钙的过程.碳酸钙的形成受到菌种、温度、pH值和钙源等因素的影响,菌种是碳酸钙沉淀形成的关键;偏离适宜的温度和pH值时酶活性会减小,甚至有可能失活及变性;与CaCl2、Ca(NO3)2等钙源相比,Ca(CH3 COO)2可以避免Ca2+团聚,从而表现出更高的矿化率.本文探讨了菌种的适用性及菌种、温度、pH值等因素对微生物沉积矿化机制的影响,并分别就MICP技术在地基砂土加固、混凝土裂纹修复、再生骨料强化等建筑领域的应用现状进行了综述,最后指出目前MICP技术在工程应用中存在的问题,并对MICP技术未来的研究方向进行了展望.     

水泥基材料中Ca2+对矿化微生物的碳酸酐酶产量、活性和矿化的影响

本工作针对一种适用于水泥基材料的耐碱矿化微生物,研究了水泥基材料中Ca²⁺浓度变化(0～5 mmol/L)对矿化微生物的产酶量、碳酸酐酶活性以及诱导CaCO₃矿化能力的影响。对分离纯化不同Ca²⁺浓度菌液中的碳酸酐酶进行酶产量测定,并通过测定矿化微生物的细菌生长曲线和单菌产酶量分析Ca²⁺浓度对其的影响机理;基于酯酶法测定不同Ca²⁺浓度下碳酸酐酶的活性,并利用FTIR测定官能团,分析二级结构变化和氢键变化,进而得到Ca²⁺浓度对碳酸酐酶活性的影响机理;最后基于热重分析不同Ca²⁺浓度溶液中矿化微生物的诱导矿化能力,并测定矿化产物晶形。试验结果表明,当Ca²⁺浓度为2.5 mmol/L时,矿化微生物生长增殖最快,单菌产酶量最高,因此整体酶产量最高;碳酸酐酶活性在Ca²⁺浓度为5 mmol/L时达到最大值,但Ca²⁺会破坏碳酸酐酶结构的有序性;当Ca²⁺     

一种基于微生物沉积的水泥砂浆表面改性技术

某些微生物能诱导沉积出具有胶凝和矿化作用的碳酸钙,可以用来修复和密实水泥基材料。但是目前微生物沉积技术工艺复杂,成本高,不利于推广和工程应用。尝试采用水泥砂浆粉作为覆膜载体,利用巴斯德芽孢杆菌对水泥砂浆进行表面处理。研究结果表明,采用该方法能使巴斯德芽孢杆菌在水泥试块表面诱导沉积出碳酸钙,有效减少水泥砂浆的吸水性能。当微生物采用含有尿素的培养基培养时,表面改性后的水泥砂浆吸水系数降低了58%。采用压汞测试仪(MIP)分析了处理前后水泥试块表层的孔隙率以及孔结构特征。发现采用巴斯德芽孢杆菌处理后,样品孔隙率显著降低,大孔的含量显著减少,当微生物采用含有尿素的培养基培养时,总孔隙率降低了40%。X射线衍射仪(XRD)和场发射扫描电镜(SEM)分析表明,经微生物技术处理后水泥试块内部的孔洞和裂缝被球霰石和方解石填充。     

脲解型微生物诱导碳酸钙沉积研究

研究了钙源种类对脲解型微生物诱导碳酸钙沉积的生物-化学过程的影响。利用电位分析法实时测试了沉积过程中钙离子、铵离子及pH值的变化,并利用显微计数对细菌浓度进行了监测。采用扫描电镜(SEM)、X射线衍射(XRD)和分析红外光谱(IR)对沉积产物进行了研究。结果表明,不同钙源环境下脲解型微生物诱导矿化沉积都存在化学沉淀、微生物诱导矿化沉积和沉淀完全3个阶段;有机钙源环境下细菌的产矿动力比在无机钙源中高,且两种钙源所获得的方解石晶体沉积物在形貌上差异显著。     

微生物水泥基材料的红外光谱研究

微生物水泥是在节能减排大环境下而研发的一种新型生物水泥。利用X射线衍射(XRD)、透射电镜(TEM)和红外光谱(IR)分别对微生物水泥基材料的成分、形貌、微观结构进行了研究。TEM分析表明,微生物水泥基材料内部微观结构与化学法浇注的砂颗粒内部微观结构不同。微生物矿化形成的方解石可以胶结松散颗粒,而化学法形成的方解石与松散颗粒之间存在孔隙,不能胶结松散颗粒;IR分析表明,微生物水泥基材料中的Si—O键和C—O键频率均发生红移,而化学法浇注的砂颗粒中Si—O键和C—O键频率未发生改变,另外,化学法浇注的砂颗粒中Si—O键与单纯石英砂中的Si—O键频率相同。     

微生物矿化沉积技术强化核壳结构再生粗骨料

为实现废弃混凝土砂粉的高效利用,以废弃砂为内核,废弃粉及少量胶凝材料为壳层原料,采用冷粘成球技术制备核壳结构再生粗骨料,并利用微生物矿化沉积碳酸钙(MlCP)提升骨料品质,本工作研究了矿化时间、钙离子浓度对内核质量增加率、吸水率的影响,及微生物矿化剂对再生粗骨料性能的提升效果,通过SEM、TG-DTG分析再生粗骨料内核及表面形貌、物相含量.结果表明,矿化微生物可加速、诱导碳酸钙沉积,密实结构,显著提升再生粗骨料品质;当微生物矿化剂掺量为1.0％(质量分数)时,再生粗骨料压碎指标、吸水率、微粉含量、质量损失率分别降低50.0％、21.2％、50.0％、15.3％,表观密度增加2.8％,壳层氢氧化钙完全矿化,碳酸钙含量增至24.18％.     

低碱性材料负载微生物芽孢修复水泥基材料后期裂缝

选用低碱性的硫铝酸盐水泥(SAC)作为载体来负载微生物芽孢,对比研究浸泡在水泥基材料模拟孔隙中不同时间后,SAC负载保护和无负载的微生物芽孢的复活能力。同时研究了开裂龄期为90 d时SAC负载微生物对砂浆试件后期裂缝的自修复效果,并对其自修复机理进行了详细的探讨。研究结果表明：在水泥基模拟孔隙溶液中,与未负载的芽孢相比,SAC负载芽孢具有更好的保护效果,在水泥基材料模拟孔隙溶液浸泡90 d后,芽孢仍具有良好的活性。对于0.3～0.4 mm的砂浆裂缝,经28 d的修复养护后,面积修复率高达100%,渗水系数下降两个数量级,裂缝平均修复深度为2 246.9μm。水泥基材料裂缝的自修复过程主要是通过微生物矿化作用来实现的。     

微生物矿化沉积对再生骨料界面过渡区的影响

骨料-水泥浆体的界面过渡区疏松多孔是导致再生骨料与天然骨料性能差异的重要原因。通过试验研究微生物矿化沉积技术对再生骨料界面过渡区性能的影响。使用水泥净浆包裹不同菌种和不同方式处理的再生骨料,养护后破碎获得骨料-水泥界面过渡区,通过SEM观察界面过渡区的微观形貌变化,利用纳米压痕试验测量界面过渡区的弹性模量和硬度,并结合再生砂浆块的抗压、抗折强度试验结果,分析微生物矿化沉积对再生骨料界面过渡区的改善效果。结果表明:再生骨料经假坚强芽孢杆菌和嗜碱芽孢杆菌处理后所制备的再生砂浆块的抗压、抗折强度及再生骨料界面过渡区的弹性模量和硬度均有明显提升,两菌种矿化生成碳酸钙的能力不同造成了性能提升效果的差异。     

Influence of finely ground limestone on cement hydration

Some work has been carried out on the effect of calcium carbonate on cement paste, but there is no general agreement on the relative effects of different amounts of calcium carbonate on cement paste properties. The objective of the present work is to assess the effect of various amounts of calcium carbonate on the hydration of tricalcium silicate in order to explain the physico-chemical changes occurring during Portland cement hydration. It is shown that calcium carbonate has an accelerating effect on C₃S and cement hydration and leads to the precipitation of some calcium carbosilicate hydrate.     

基于生物矿化机理的自愈合混凝土制备与表征

研究旨在利用微生物诱导碳酸钙沉淀机理,研制新型细菌自愈合混凝土。在高pH条件下培养,筛选出一组与枯草芽孢杆菌相关的产芽孢杆菌。将筛选得到的耐碱枯草芽孢杆菌M9进行生物矿化沉淀测试,X射线衍射(XRD)和扫描电镜(SEM),结果表明沉淀矿物为呈方解石形态的碳酸钙。以枯草芽孢杆菌M9为修复剂,掺入聚乙烯醇(PVA)纤维制备自愈合混凝土梁试件。利用引气剂在水泥净浆混合料中产生微孔,为微生物提供生态位。对养护14 d的混凝土梁试件进行三点弯曲试验,获得宽度约为0.3 mm的裂纹。28 d后,细菌代谢等作用形成碳酸钙晶体填充物自动填充微裂纹空隙。后续SEM测试表明:方解石是裂纹填充矿物主要形态,且晶体表面残留部分细菌印记。愈合后的混凝土梁在第二次弯曲测试下的抗弯强度提高了约14%,该强度恢复是通过修复基体裂纹和纤维-基体界面的粘结力来实现的。     

Incorporating carbon sequestration materials in civil infrastructure: A micro and nano-structural analysis

The Calera method for carbon sequestration promotes carbon mineralization through aqueous precipitation. This work reports a comprehensive analysis on a carbonate obtained by the Calera process to evaluate its suitability as a cement replacement for concrete applications. This work focuses on the analysis of two hydrated cement pastes made with a blend of Portland cement and Calera carbonates by various advanced analytical techniques. Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) was used to observe microstructures and determine elemental compositions. The synchrotron X-ray diffraction technique combined with Rietveld analysis were applied to identify constituent phases and refine crystal structures, crystallite sizes as well as relative phase abundances. Calcite and vaterite are observed in all samples while CSH II and portlandite are dominant in the cement pastes. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectrometry and Scanning Transmission X-ray Microscopy (STXM) experiments were conducted to investigate chemical speciation and morphological information of carbonate minerals with different absorption energies. STXM results confirmed heterogeneity of the samples, and also provided a nano-scale phase map across multiple particles. Differential Thermogravimetric (DTG) was used to observe heat transfer through structures and changes in mass upon heating. A compressive strength tests were performed on materials and shown comparable strength to Portland cement.     

Modification of cement hydration at early ages by natural and heated wood

Heat treatments of wood are widely used for the reduction of wood swelling and dimensional instability of wood–cement composites. The effect of natural and heated wood on the hydration of cement at early ages was investigated by isothermal calorimetry, thermogravimetry (TGA) and Fourier transform infrared (FTIR) spectroscopy. The addition of wood strongly delays and inhibits the hydration of the silicate phases. Consequently, the amount of portlandite is lower in composites than in neat cement. Approximately 30% of the inhibition of portlandite precipitation is due to an increase of calcium carbonate content in cement paste. The absorption of a part of water by wood produces a decrease in gypsum consumption. Nevertheless, the ettringite formation is not significantly affected since a diffusion of sulfate ions from wood occurs.     

电石渣的综合利用及制备轻质碳酸钙的研究进展

简述了电石渣在生产水泥等化工产品、环保等方面综合利用的现状，并重点评述了以电石渣为原料制备轻质碳酸钙和纳米碳酸钙的研究进展。以电石渣为原料生产有较高附加值的轻质碳酸钙和纳米碳酸钙，具有重要的开发价值。     

Degradation kinetics and aging mechanisms on sisal fiber cement composite systems

The kinetics of vegetable (sisal) fiber degradation and the mechanisms responsible for deterioration of continuous sisal fiber cement composites are presented in this paper. Two matrices were used: one with 50% partial cement replacement by metakaolin (PC–MK) and a reference matrix having as binder only Portland cement (PC). The durability performance of the composite systems is examined and the mechanisms for the significant delay in the fiber degradation when the total amount of calcium hydroxide is reduced from the matrix discussed. The composites were subjected to 5, 10, 15, 20 and 25 cycles of wetting and drying and then tested under a four point bending load configuration in order to determine the flexural behavior and cracking mechanisms with progressive aging. Furthermore, composites stored under controlled lab conditions were tested under bending load at ages ranging from 28 days to 5 years. Fibers extracted from the aged composites were subjected to thermal analysis, Fourier transform infrared spectroscopy and microscopical observations in order to evaluate the changes in chemical composition and microstructure. Two fiber degradation mechanisms were observed in the PC composites: fiber mineralization due to the precipitation of calcium hydroxide in the fiber cell and surface and degradation of cellulose, hemicellulose and lignin due to the adsorption of calcium and hydroxyl ions. The degradation process occurs rapidly and after 10 cycles of wetting/drying a quite expressive modification in the flexural behavior is observed. The residual mechanical parameters after 25 cycles were the same as those observed in the unreinforced matrix. For the PC–MK composite fiber mineralization was not observed due to the low content of CH in the matrix.     

Self-healing of surface cracks in mortars with expansive additive and crystalline additive

This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca²⁺ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca²⁺ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.     

Interactions between superabsorbent polymers and cement-based composites incorporating colloidal silica nanoparticles

The relatively new applications of superabsorbent polymers (SAPs) in cement based materials call for investigations regarding their behaviors in relation to other constituents in the system. Colloidal silica nanoparticles (CS) are becoming increasingly important for the improvement of strength and durability of cement based materials. In this study, a poly (AA-co-AM) SAP was synthesized by free radical polymerization, and its behaviors in cement based composites incorporating CS were investigated. These included swelling behavior, setting time, mechanical performance in different curing conditions, and rheological properties of fresh pastes. The observation of an unusual reduction in swelling, revealed the role of SAP in precipitation of calcium carbonate from the cement paste filtrate, and provided evidence for the less than expected reduction in workability and setting times. Combinations of the SAP and CS increased the compressive and decreased the flexural strengths, respectively, which is supported by changes in the microstructure as observed by SEM.     

Evaluation of colloidal silica suspension as efficient additive for improving physicochemical and in vitro biological properties of calcium sulfate-based nanocomposite bone cement

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60 wt% α-calcium sulfate hemihydrate and 40 wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous colloidal silica suspension (20 wt%). In this study, the above mentioned powder phase was mixed with distilled water to prepare a calcium sulfate/nanoapatite composite without any additive. Structural properties, setting time, compressive strength, in vitro bioactivity and cellular properties of the cements were investigated by appropriate techniques. From X-ray diffractometer analysis, except gypsum and apatite, no further phases were found in both silica-containing and silica-free cements. The results showed that both setting time and compressive strength of the calcium sulfate/nanoapatite cement improved by using colloidal silica suspension as cement liquid. Meanwhile, the condensed phase produced from the polymerization process of colloidal silica filled the micropores of the microstructure and covered rodlike gypsum crystals and thus controlled cement disintegration in simulated body fluid. Additionally, formation of apatite layer was favored on the surfaces of the new cement while no apatite precipitation was observed for the cement prepared by distilled water. In this study, it was also revealed that the number of viable osteosarcoma cells cultured with extracts of both cements were comparable, while silica-containing cement increased alkaline phosphatase activity of the cells. These results suggest that the developed cement may be a suitable bone filling material after well passing of the corresponding in vivo tests.     

Synthesis of calcium hydroxyapatite from calcium carbonate and different orthophosphate sources: A comparative study

The synthesis of calcium hydroxyapatite (Ca-HA) starting from calcium carbonate and different orthophosphate sources, including orthophosphoric acid, potassium, sodium and ammonium dihydrogen orthophosphates, was investigated under ambient conditions. The reaction started with calcium carbonate dissolution in an acid medium, followed by rapid precipitation of calcium cations with orthophosphate species to form calcium phosphate based particles which were in the size range of 0.4–1 μm. These particles then agglomerated into much larger ones, up to 350 μm in diameter (aggregates). These aggregates possessed an unstable porous structure which was responsible for the porosity of the final products. The highest specific surface area and pore volume were obtained with potassium dihydrogen orthophosphate. On the other hand, orthophosphoric acid led to the highest dissolution of calcium carbonate and the complete precipitation of orthophosphate species. Under ambient conditions, calcium phosphate based solid products of low crystallinity were formed. Different intermediates were identified and a reaction pathway proposed.