Microbial Cementation Research Articles

Bacteria를 이용한 실트와 모래의 고결화에 따른 탄산칼슘 확인

본 연구의 목적은 연약지반에 대한 미생물의 고결화 메커니즘을 확인하기 위함이다. 연약지반에 대한 미생물의 고결화 메커니즘을 확인하기 위해서 6가지 미생물 조건(무처리, 일반농도처리, 고농도처리, 상층액처리, 2X 고농도처리, 25% 시료 고농도처리)으로 실험되어졌다. 전자현미경(SEM, EDX)과 X선 분석 회절기(XRD)를 이용하여 실트질시료와 느슨한 모래시료의 분석을 수행하였으며, 일반농도처리 시료에 비교하여 25% 시료 고농도처리 시료에서 입자와 입자 사이에 탄산칼슘이 더욱 명확히 관찰되어졌다. 이러한 연구결과를 바탕으로 연약지반에 대한 미생물 고결화 반응을 확인할 수 있었다. The purpose of this study is to understand the mechanism of cementation of soil induced by bacteria. In order to understand the mechanism of cementation of soft soils treated with bacteria, six types of specimens(Not treated, Normal concentration bacteria treatment, High concentration bacteria treatment, Supernatant high concentration bacteria treatment, Double high concentration bacteria treatment, and 25% Specimen high concentration bacteria treatment) were made. Scanning Electron Microscope (SEM), EDX and X-ray diffraction (XRD) analyses were performed on the soft silt and loose sand specimens. Compared with the normal bacteria concentration treated specimen, a clearer cementation between particles was observed in the 25% specimen high bacteria concentration treated specimen. On the basis of the preliminary results, it appears that microbial cementation can occur in the soft soil.

Development of microbe cementitious material in China

Microbe cementitious material as a binder has been developed due to the ever increasing awareness of environmental protection. The new cementitious material relies on microbiologically induced precipitation of calcium carbonate to bind loose particles or repair surface defects and cracks of cement-based material. This paper elaborates the research on loose sand particles cemented by microbe cement from three aspects: compressive strength, pore structure and microstructure. In addition, the research on restoration surface defects and cracks of cement-based material by microbe cement is introduced from two parameters: surface water absorption and compressive strength recover coefficient. The results show that microbe cementitious material can bind loose particles and repair surface defects or cracks of cement-based material.

Characterization of microbe cementitious materials

A new generation of cement, microbe cement, has been developed in response to the ever increasing awareness of environmental protection. Microbe cement is a new strengthening material based on microbiologically induced precipitation of calcium carbonate. This paper confirms the feasibility of binding loose sand particles using microbe cement and details the cementation mechanism of microbe cement. We have also prepared microbe cementitious materials (biosandstones). The compressive strength of the bio-sandstone, which depends on the content of calcium carbonate produced by microbially induced precipitation and the bio-mediated calcite crystal size, could be up to 12 MPa at an age of 20 days. By increasing the precipitated calcite content, the compressive strength and microstructure of bio-sandstone could be improved.

Influence of molding process on mechanical properties of sandstone cemented by microbe cement

A new generation of cement, microbe cement has been developed due to the ever increasing awareness of environmental protection. Microbe cement is a new strengthening technique based on microbiologically induced precipitation of calcium carbonate. This paper confirms the feasibility of microbe cement binding loose sand particles and presents results from a laboratory research on the influence of molding process (non-pressure molding, pressure molding, discontinuous non-pressure molding and pumping molding) on the mechanical properties of sandstone microbe cement bound. The results showed that the ways of molding procedure had a strong influence on the mechanical properties of bio-sandstone. The strength, which was up to 12.0 MPa, of sandstone microbe cement bound by adopting pumping molding process was higher than other three processes. Meanwhile, Scanning electron microscope (SEM) image analysis technique was adopted to measure the corresponding variation of porous characteristics caused by different molding processes. The results indicate that the microstructure of bio-sandstone adopted by pumping molding has lower porosity and higher content of precipitated calcium carbonate than other three molding processes.

Microbial carbonates in Holocene beachrocks, Shuiweiling, Luhuitou Peninsula, Hainan Island

Two research methods, geomicrobiology and carbonate sedimentology, were adopted to study the microbial carbonates in the beachrocks, Shuiweiling, Luhuitou, Sanya City, Hainan Island. The results indicate that microbial carbonates occur in Shuiweiling beachrocks and cements related to microbial activitives are common. Microbial carbonates were mainly developed on the surfaces of coral skeletons and within the coral (fragments and shivers) skeletal cavities, and rarely grew in interspaces formed by coral and other biological detritus. The growth morphologies of microbial carbonates are various, including stromatolitic lamination, thin crusts, dome-like, and microbialites. Microbial carbonates commonly trap fine-sized bioclasts, contain tubular filaments, and show laminated growth striation. Microbial carbonates within the coral skeletal cavities are generally stromatolitic cone-shaped, with a random growth direction along the bearing of trend of cavities, showing distinct growth laminae and recognizable growth phases. It is a special growth pattern of crypt microbial carbonates. Microbial cements occur mainly in shape of needle cement, calcified filaments, microborings, and calcified framboidal spheres. The needle cement is the most common type. These microbial cements indicate that microbial activities and microbial carbonates played an important role in beachrock formation in which carbonates were dominant components and the climate of tropical ocean monsoon was influential. Such microbial carbonates and microbial cementation have not been reported here from beachrocks along the northern shorelines of the South China Sea. The results support a clear microbial origin for certain carbonate cements in beachrocks, confirm that microbial carbonates are a significant contributor to carbonate sedimentation, and widen the knowledge of beachrocks from a new field.

Steep microbial boundstone-dominated platform margins—examples and implications

Seaward progradation of several kilometers has been documented mostly for leeward margin low-angle carbonate slope systems with a dominant platform top sediment source. However, steep and high-relief margins fronting deep basins can also prograde and as such are somewhat perplexing. Characteristics of two prograding Carboniferous examples provide a model which may apply elsewhere: (1) outcrops in Asturias, northern Spain serve as important analogs for (2) hydrocarbon reservoirs in steep-sided isolated platforms of the North Caspian Basin, Kazakhstan, such as Tengiz. Seismic and well data from Tengiz corroborate outcrop patterns for slope development, showing progradation of up to 5 and more than 10 km, respectively, despite the high-relief (up to 600 m) and steep (∼20–35°) nature of these margins. The two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m (or more) depth and a lower slope dominated by (mega)breccias and grain flow deposits derived from the margin and slope itself. The broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform-top-derived sediment. Rapid in situ lithification of the boundstone provides stability to the steep slopes, but also leads to readjustment through shearing and avalanching. What controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins. This new model of “slope” shedding has implications for slope readjustment processes and resulting architecture, sequence stratigraphic interpretation, reservoir characterization, and reservoir modeling. Especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke, under certain stress regimes, shattering and fracturing thereby generating significant non-matrix permeability. Key considerations are the contrasts with the Bahamian high stand shedding depositional model, slope progradation rates that range from 450 to >1500 m/My, and net growth rates of in situ boundstone of ∼1000 m/My, comparable to or higher than accretion rates for metazoan skeletal reef growth.

ABSTRACT: The Role of Microbial Boundstones and Carbonate Cements in the Sedimentary Dynamics of Middle-Upper Triassic Slopes from the Southern Alpine Dolomites

ABSTRACT: The Role of Microbial Boundstones and Carbonate Cements in the Sedimentary Dynamics of Middle-Upper Triassic Slopes from the Southern Alpine Dolomites

Sediments and stromatoporoid morphotypes in Ludfordian (Upper Silurian) reefal sea stacks on Gotland, Sweden

A study of the sedimentology and stromatoporoid morphologies in the Upper Silurian of southeastern Gotland reveals a strong relationship between the depositional environment and the morphological range of stromatoporoids. In high-energy environments, characterised by packstones and grainstones, low-profile forms dominate, whereas in calmer settings, characterised by wackestones and packstones, high-profile stromatoporoids dominate. Four rock units are recognised, representing two major facies: Reef-like limestones and Detrital grain-stones. Reef-like limestones comprise a variety of lithologies including wackestones, packstones, boundstones, and framestones. All units are shallow marine, but the occurrence of crystal silt may indicate a vadose situation on top of the reef-like facies. In the reef-like units, hard substrates for stromatoporoid growth were probably provided by microbial cementation. Sedimentation rates were generally low although episodic high sedimentation occurred as indicated by raggedness in stromatoporoid skeletons. The stromatoporoid fauna is considered a low-diversity assemblage dominated by Parallelostroma typicum.

The underlying substrate ofthe Cerin Lithographic Limestones

The Cerin Lithographic Limestones do not cover a wide area. They correspond to numerous lagoon in-fillings of limited development, within a wide emerged area characterized by sandy (skeletal) limestones mainly of coral origin (Landaize Limestones). At the village of Cerin where an excavation for paleoecological studies is located, the sandy Landaize Limestones provide the lithographic limestone substrate. Their cementation is partly of supratidal and/or intertidal origin, but frequently shows phreatic freshwater features. Finally, microbial cements (bacteria or cyanobacteria) reflect a major process of lithification. The original substrate consisted of grainstones, the top of which was considerably eroded, producing uneven relief with steep slopes and even cliffs, sometimes reaching several metres in height. The erosion processes were probably mechanical in origin, but also biochemical (biokarst) and especially biological (bioerosion by grazing, boring and microbial erosion). Lime mud which produced the lithographic limestones filled the hollows between the substrate reliefs. Around areas where the uneven rocky substrate had steep gradients locally developed gravity flows occur. These are capped with microbial films which are affected by superficial slides showing more or less concentric or complex wavy structures. Locally, true slumps giving rolls and synsedimentary microfolds also occur.