Topic：Bio-cementation for Soil Improvement and Constructional Material Development
Speaker: Prof.Lin Li, Jackson State University
Chair: Prof.Jiemin Zhan
Time: Tuesday, 15th.May,2018, 16:00pm
Venue: Room B403, School of Engineering, East Campus, SYSU
报告摘要：生物固化技术是一种在自然环境中，依赖非致病菌发生的新兴的、环境友好型土壤改良技术。其中为我们所熟知的是微生物诱导碳酸盐沉淀技术(MICP)。MICP技术是通过微生物诱导而产生的碳酸盐将砂粒粘结起来，从而提高其的工程特性。本研究旨在1）对比研究细菌和脲酶诱导碳酸盐沉淀过程中的各种因素的影响；2）研究样品中随机分布的纤维对其机械特性的影响；3）进一步探究MICP技术制成的生物梁的工程特性。控制其他变量相同，分别采用Sporosarcina pasteurii菌种和脲酶来处理砂石样品，其无侧限抗压结果表明菌液/脲酶浓度、粘结液浓度、反应时间和砂石类型对样品有显著的影响，而试验进行中的环境条件的影响较小。细菌处理得到的样品无侧限抗压强度可以达到1.76-2.04 MPa, 是脲酶处理得到的样品强度的5倍左右。添加纤维后，细菌处理得到的样品 的剪切强度，柔软性和破坏应变都有很大提高。随着纤维含量达到0.3%， MICP样品的无侧限抗压强度、抗剪切强度逐渐提高。最佳的纤维加入量为0.2-0.3%。 此时，MICP的无侧限抗压强度为不加纤维样品的2倍多。同时，其破坏应变也提高到3倍以上。纤维的掺入不仅提高了样品的残余应力，同时也降低了MICP处理样品的易碎特性。细菌处理后的生物梁样品的试验结果显示，其弯曲强度为950kPa，达到水泥砂石梁的20%-25%，同时高于石灰砂石梁的30%。而且，MICP处理得到的生物梁无侧向抗压强度为1300kPa，高于水泥砂石梁强度（900kPa）的10%， 并远远高于石灰砂石梁的强度（140kPa）。扫描电子显微镜图片显示，MICP处理样品、水泥处理样品及石灰处理样品的破坏为粘接颗粒的破坏。
Abstract: Bio-cementation is a promising and environmentally innocuous technology to improve soil engineering properties. It is naturally happened and induced by nonpathogenic organisms which are native to soil environment. One common bio-cementation process is the microbial induced calcite precipitation (MICP), which can bond sand grains together and improve the engineering properties of soil. The objectives of this study were 1) to investigate the influence of various factors on engineering properties of MICP-treated soil catalyzed by bacteria and ureases, 2) to investigate the effect of randomly distributed discrete fiber on the mechanical properties of MICP-treated soil and to discover the corresponding mechanisms, and 3) to explore the bio-beam through MICP. The experiments of MICP catalyzed by Sporosarcina pasteurii and urease were conducted in similar conditions. The results of unconfined compression test show that the experimental factors (bacteria/urease concentration, cementation media concentration, reaction time, and type of sand) have significant impact on the MICP process and engineering properties of sand treated by both bacteria and urease, while the curing conditions has small effect. The unconfined compression strength (1.76~2.04 MPa) of bacteria treated samples is almost 5 times that (0.33~0.43 MPa) of urease treated samples under similar urease activity. The MICP process catalyzed by bacteria is much more effective than the one catalyzed by urease in terms of engineering soil properties improvement. The results showed that remarkable improvements in shear strength, ductility, and failure strain were achieved with fiber addition in the MICP-treated sand. The UCS and shear strength increased gradually with an increase in fiber content up to a fiber content of 0.3%. The optimum fiber content in the MICP-treated sand was found to be 0.2%-0.3%. The UCS of MICP-treated sand at the optimum fiber content is more than 2 times higher than that without addition of fiber. The failure strain of MICP-treated sand at the optimum fiber content is nearly 3 times higher than that without addition of fiber. The inclusion of fibers increases the residual strength occurring after peak stress and decreases the brittle behavior of the MICP-treated sand. The test results indicated that flexure strength of MICP-treated bio-beam was 950 kPa which was similar to flexure strength of 20%-25% cement-treated sand beams, but was much higher than flexure strength of 30% lime-treated sand beams. The unconfined compression test results showed that the UCS of MICP-treated bio-beam (1300 kPa) was higher than UCS of 10% cement-treated specimen (900 kPa), and much higher than UCS of lime-treated sample (around 140 kPa). SEM images showed that failure pattern of MICP-treated, cement-treated and lime-treated specimens were bond-particle failure.
Dr. Lin Li, P.E., Fellow of ASCE, Professor in the Department of Civil and Environmental Engineering at Jackson State University. He got his PhD from University of Wisconsin-Madison under Prof. Craig Benson in 2004. After 1 year postdoc working experience with Prof. Tuncer Edil in 2005, he started his academic career in Jackson State University. He teaches geotechnical engineering courses, including foundation engineering, unsaturated soil mechanics, geoenvironmental engineering, advanced soil mechanics, and soil dynamics. His expertise is in innovative levee testing and protection, bio-mediated ground improvement, sustainable infrastructure and geo-environmental area. He has been principal investigator or co-principal investigator of more than fifteen major research grants from federal and state agencies with total funding amounts of $4.1 Million, including National Science Foundation, Department of Homeland Security, US Army Corps of Engineer, US Department of Transportation, Mississippi DOT, Recycled Materials Resource Center under Federal Highway Administration, Institute for Multimodal Transportation under Federal Transit Administration, mostly in the area of geotechnical engineering. Dr. Li is the author or co-author of more than 105 peer-reviewed published articles with total citation of 1957 (h-index 10). With funding support from DHS, Dr. Li’s research focuses on levee protection during the Hurricane overtopping. He has published 30 scientific papers about innovative levee strengthening and testing under full scale overtopping conditions. With funding support from NSF, Dr. Li’s research on bio-mediated ground improvement leads to more than 10 SCI-index journal articles. He got HEADWAE Award from State of Mississippi in 2017, Faculty Excellence Award Richard from JSU in 2014, and in 2015, Richard S. Ladd D18 Standards Development Award from ASTM for his effort in ASTM D7762 development. He is editorial board member of Journal of Geotechnical and Geological Engineering. He is vice chair of TRB AFP40 committee, chair of ASTM D18.14 committee, and member of ASCE committees.