Late Holocene to Recent aragonite-cemented transgressive lag deposits in the Abu Dhabi lagoon and intertidal sabkha

Modern cemented intervals (beachrock, firmgrounds to hardgrounds and concretionary layers) form in the lagoon and intertidal sabkha of Abu Dhabi. Seafloor lithification actively occurs in open, current-swept channels in low-lying areas between ooid shoals, in the intertidal zone of the middle lagoon, some centimetres beneath the inner lagoonal seafloor (i.e. within the sediment column) and at the sediment surface the intertidal sabkha. The concept of ‘concretionary sub-hardgrounds’, i.e. laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary, is introduced and discussed. Based on calibrated radiocarbon ages, seafloor lithification commenced during the Middle to Late Holocene (ca 9000 cal yr bp ), and proceeds to the present-day. Lithification occurs in the context of the actualistic relative sea-level rise shifting the coastline landward across the extremely low-angle carbonate ramp. The cemented intervals are interpreted as parasequence boundaries in the sense of ‘marine flooding surfaces’, but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited. Aragonite, (micritic) calcite and, less commonly, gypsum cements lithify the firmground/hardground intervals. Cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography, cathodoluminescence microscopy and Raman spectroscopy. The morphology of aragonitic cements changes from needle-shaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar, lath and platy crystals in the inner lagoon. Precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology. Data shown here shed light on ancient, formerly aragonite-cemented seafloors, now altered to diagenetic calcites, but also document the complexity of highly dynamic near coastal depositional environments.     

海相软土场地水泥土劣化机理室内试验研究

将水泥土和周围土体作为研究对象,利用室内化学分析试验得到了离子浓度的时空分布规律,并从腐蚀离子干预水化反应进程和分解水化产物两个过程揭示了海相软土场地水泥土劣化机理。Ca^2+由水泥土向土体中扩散,Mg^2+、SO42^-及Cl^-从土体向水泥土扩散;随着水化反应的进行,Ca^2+不断生成,水泥土中足够多的Ca^2+是保证水化反应进行并维持水化产物稳定的必要条件,Ca^2+不断向土体扩散是水泥土劣化的原因之一;水泥土内部的SO42^-及Cl^-在浓度较低(分别低于9和15 g/L)时有利于水泥土强度的提高,浓度较高时则导致水泥土发生胀裂;水泥土中Mg^2+的存在会阻碍水化产物的生成并分解水化产物,但浓度较低(低于3 g/L)时,影响不明显;土体中Mg^2+、SO42^-及Cl^-浓度高于水泥土中的浓度,在水泥土表层与水化产物反应生成胶结性差及膨胀性高的物质,促使水泥土劣化。     

氢氧化镁煅烧工艺和原料配比对氯氧镁水泥抗压强度的影响

以电石渣和MgCl_2制备的Mg(OH)_2为原料,制备氯氧镁水泥(MOC)用活性MgO,通过正交实验的方法观察煅烧温度、保温时间、活性MgO与MgCl_2摩尔比、H_2O与MgCl_2摩尔比对MOC试件抗压强度的影响。以3d、7d、28dMOC试件的抗压强度为评价指标,综合各因素对抗压强度的影响趋势发现:随煅烧温度及活性MgO与MgCl_2摩尔比的增加,MOC试件抗压强度呈增加趋势;保温时间大于30 min时,MOC试件的抗压强度随保温时间增加而降低;随H_2O与MgCl_2摩尔比的增大,试件的抗压强度逐渐减小。且不同龄期内,H_2O与MgCl_2摩尔比对试件抗压强度影响最为显著。当煅烧温度为600℃,保温时间为30 min,MgO与MgCl_2摩尔比为8,H_2O与MgCl_2摩尔比为13时,试件的抗压强度最佳。     

Study of elastic-plastic damage model of cement consolidated soil with high organic content

On the basis of elastic-plastic damage model of cement consolidated soil, the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and parameters in the equation, and established the elastic-plastic damage model of cement consolidated soil considering organic contents. The results show that the parameters change correspondingly with difference of the organic contents. The higher the organic contents are, the less the valves of the parameters such as elastic modulus (E), material parameters (K, n) and damage evolution parameter (ε) become, but the larger strain damage threshold value (εd) of the sample is. Meanwhile, the calculation results obtained from established model are compared with the test data in the condition of common indoors test, which is testified with reliability.     

地方病高发区成井用胶质水泥浆的试验研究

通过地方病高发区成井用胶质水泥浆的试验研究，以普通水泥和膨润土为基本材料，同时添加改善材料性能的外加剂，研制了一种用于高砷、高氟、高矿化度地区水井成井的止水材料，具有流动性好、抗渗性高、不收缩、完全无毒、价格低廉等特点，特别是其高抗渗性和不收缩性非常适合地方病区成井时隔离劣质含水层，保证优质含水层与劣质含水层互不串通、不渗漏、不污染。     

Mn content of reservoir calcite cement: A novel inorganic geotracer of secondary petroleum migration in the tectonically complex Junggar Basin (NW China)

Electronic probe microanalysis(EPMA) results of reservoir calcite cement from fourteen core samples in the Junggar Basin show that Mn-content varies largely between different samples from below the detect limitation to 4.14%,while it displays a generally good correlation with oil-gas shows.This,therefore,likely indicates that concentration of the Mn-content of the calcite cement has a close rela-tion to the intensity of petroleum fluid charging during hydrocarbon secondary migration.In order to assess this hypothesis,oxygen and strontium isotopic measurements on sixteen calcite veins host in source sequences were carried out to investigate the feature of the oil-source petroleum fluid.Analytical results imply that during hydrocarbon generation and migration,deep hot fluid has dissolved volcanic minerals interlined between mudstone source rocks.As Mn is a kind of typical trace element enriched in volcanic rocks,it is reasonable to conclude that the petroleum fluid formed in the source sequences would be Mn-rich.Consequently,calcite cements precipitated from such Mn-rich petroleum fluid would be Mn-rich accordingly.Due to the geologic chromatographic effect during migration along reservoir rocks,the decreasing of the Mn-content of the reservoir calcite cements indicates the migration direction.Then,this novel geotracer was further successfully applied in the study of hydrocarbon migration in the Junggar Basin in combination with organic geochemical analyses during the hydrocarbon migration.The Mn content of the reservoir calcite cement appears promising as a novel inorganic geotracer for the petroleum migration.This paper represents a search for novel indicators of secondary petroleum migration in tectonically complex basins based on fundamentals of the reservoir fluid-rock interactions.     

Utilization of Basic Oxygen Furnace (BOF) slag in the production of a hydraulic cement binder

Basic Oxygen Furnace (BOF) slag is a major waste product generated during the steelmaking process. In India and in most industrial countries, the use of BOF slag as a road ballast and land filler has had a very long history. This being a low end use, a study was conducted to examine the possibility of converting the slag into a hydraulic binder. This paper describes the effect of cooling rate on mineralogy and cementing characteristics of normal BOF slag as well as iron oxide-devoid BOF slag. Specifically, the mineralogy and compressive strengths of heat-treated slags were compared with a conventional ordinary Portland cement. It was found that the slowly cooled slags did not show any cementing properties. The iron oxide-devoid slag, on slow cooling, disintegrated into fine powder. The water-cured cubic specimens of quenched slag products were tested for their compressive strengths. The cementing properties of the quenched slag products were improved by formation of hydraulic phases and showed considerable strength after 28 days of water curing.     

水泥-水玻璃浆材在灌浆工程中的应用

水泥-水玻璃作为一种复合型灌浆材料,集中了水泥和水玻璃两种灌浆材料的优点,在许多灌浆工程中发挥了重要作用。本文从水泥、水玻璃的基本性能出发,对水泥-水玻璃灌浆材料的性能和应用进行了探讨     

粉喷桩工程性状试验研究

对水泥加固土的工程特性进行了系统的研究。 现场开展了粉喷桩单桩及复合地基静载试验, 对粉喷桩复合地基承载力、桩土应力比及单桩荷载传递规律进行了分析和研究。取得了一些有益的结果, 这些结果对粉喷桩工程实践具有指导意义     

砂岩中石英胶结物的成因及其研究意义

次生加大石英胶结物是砂岩中最的胶结物之一。石英胶结物的时空分布表现在越年轻的地层石英胶结物的含量越少,随埋深增加石英胶结物的含量增加,而且盆地类型也是控制石英胶结物含量的一个不可忽视的因素。石英胶结物的硅质来源有很多种说法,但是区域上可能以某一种或某几种来源为主。影响石英胶结物沉淀的主要因素有温度流体的ｐＨ值等;而关于孔隙流动与硅质搬运和沉淀有三促假说,即：浅部地下水循环说、压实驱动流体高度集中说