Function Of Cement Research Articles

Fracture of bio-cemented sands

Bio-chemical reactions enable the production of biomimetic materials such as sandstones. In the present study, microbiologically-induced calcium carbonate precipitation (MICP) is used to manufacture laboratory-scale specimens for fracture toughness measurement. The mode I and mixed-mode fracture toughnesses are measured as a function of cementation, and are correlated with strength, permeability and porosity. A micromechanical model is developed to predict the dependence of mode I fracture toughness upon the degree of cementation. In addition, the role of the crack tip T-stress in dictating kink angle and toughness is determined for mixed mode loading. At a sufficiently low degree of cementation, the zone of microcracking in the vicinity of the crack tip is sufficiently large for a crack tip K-field to cease to exist and for crack kinking theory to not apply. The interplay between cementation and fracture properties of sedimentary rocks is explained; this understanding underpins a wide range of rock fracture phenomena including hydraulic fracture.

Characterization, controlling factors and evolution of fracture effectiveness in shale oil reservoirs

Fracture effectiveness is of great significance for seeking shale oil exploration targets. The fracture effectiveness and primary controlling factors in the Cretaceous Qing-1 Member shale oil reservoir in Gulong Sag, China, was evaluated based on precise fracture characterization on core samples and thin sections. The evolution sequence of fracture effectiveness was subsequently discussed. Structural fractures, diagenetic fractures and overpressure fractures are found in the study area, where structural fracture is the most important ones, which is characterized by high density, large aperture and weak filling. Structural fractures were formed in three stages and underwent two filling events, while fractures growing at the third stage with no filling are the most effective ones. Diagenetic fractures can be classified into bedding-parallel fractures and stylolites, where the former is partly filled, and the latter is fully filled by dark minerals. Hence, these fractures can act as seepage barriers. The overpressure fractures have large apertures but short length and are insensitively filled. Fracture effectiveness varies greatly as a function of cementation, fracture growth period, dissolution, tectonic activity at later stage, abnormal high pressure and current tectonic stress field. Fractures developing at earlier stage are commonly filled, which tends to be ineffective. Structural inversion at a later stage, abnormal high pressure and dissolution can reopen fractures and improve their effectiveness. The fractures parallel to the current maximum principal stress with high dip-angle have large apertures and good effectiveness. • Proposed a quantitative characterization method for fracture effectiveness. • Evaluated the effectiveness of fractures in shales of Gulong Sag, China. • Discussed the controlling factors and evolution of fracture effectiveness.

Substitution Local Resources Basalt Stone Scoria Lampung, Indonesia, as a Third Raw Material Aggregate to Increase The Quality of Portland Composite Cement (PCC)

Domestic cement demand is increasing in line with the increase of development of property sector and construction sector. Cement is one of the important components in making a permanent building. The function of cement in a construction is as an adhesive material that affects the strength of a building. The process of making cement is divided into two groups, namely hydraulic cement and non-hydraulic cement. Hydraulic cement consists of Portland type cement and PCC type cement, PPC cement and slag cement. The type of PCC cement (Portland Composite Cement) is produced from grinding clinker with gypsum with the addition of third raw material. The purpose of this research is to know the effect of cement quality improvement with substitution of basalt scoria stone raw material as much as 0-10% as the third raw material. The source of basalt scoria stone originated from Lampung Timur, Indonesia. The fineness test showed cement fineness was 2983-3665 cm2/gr with minimum SNI standard 2800 cm2/gr. Residue test meets the requirements of SNI standard that is equal to 16,07% -18,55%. The compressive strength test was performed at ages 3, 7 and 28 days and obtained the result that the optimum compressive strength produced was 235, 314, 394 kg/cm2. Basalt rock usage as substitution material in cement production can decrease environmental pollution caused by clinker production. Based on the cost estimation analysis, the use of basalt stone can decrease the production cost which impact on the increase of profit

Influence of cement content on the thermal properties of compressed earth blocks (CEB) in the dry state

The Compressed Earth Block (CEBs) is one of the kinds of building materials which stabilized by cement. Soil is a basic component, a renewable, non-toxic and natural resource. Samples must be stabilized with a limited percentage of cement so that samples do not lose their natural properties including thermal comfort and on other hand offer high mechanical resistance. The objective of this work is to study the effect of cement content on thermal behavior of the building material of CEBs in the dry state, by studying variation of temperature with time, and measuring thermal conductivity and the specific heat, with respect to the various cement ratios added to the samples. This study is mainly an experimental and numerical, to determine how the thermal behavior evolves with the cement content in the samples CEBs. The soil was extracted from the famous city Fez in Morocco, Fez is known for its several historical monuments and buildings. After determining its granulometry and other specific characteristics, the CEBs are made by mixing soil with cement. The samples are put in plastic bags for two weeks, then removed the plastic bags from the samples and let them to dry again for an additional two weeks away from direct sun. The samples CEBs are taken cylindrical form (8 cm diameter with an average height of 12 cm).The experimental method consists of a hot ring for which a numerical modelization was developed to fit the mathematical equations of heat diffusion and the boundary conditions. For the numerical model Bouabid and Cherraj have developed numerical model which allow, with a good accuracy, to quantify the evolution of the thermal behavior of the earth material in function of cement content.Indeed, the study provides information on the influence of the cement percentage on the thermal behavior of the samples CEBs, the thermal behavior of samples increase with increase cement content.

Investigation and Prediction Model for the Dynamic Modulus of Asphalt Emulsion Cold Recycled Mixtures

AbstractThe stiffness characteristics of four types of asphalt emulsion cold recycled mixtures (AECRMs) were evaluated using the simple performance test (SPT). Factors influencing the dynamic modulus and the applicability of the Witczak model were investigated. Based on the time-temperature superposition principle, the dynamic modulus |E*| master curves of recycled mixtures were constructed using nonlinear-least squares regression techniques. Statistical significance on the basis of one-way analysis of variance was evaluated as a function of cement, aggregate gradation, frequency, temperature, and confining pressure. The Witczak model is suitable for AECRMs and cement-treated AECRMs, and its prediction accuracy was improved by modifying the original Witczak model. The accuracy of the predicted models was evaluated on the basis of the statistical analysis. The one-way analysis of variance results indicated that the constructed master curves were consistent with the experimental test data. Frequency and tem...

Control of Cracking in Bridge Decks: Observations from the Field

Abstract Crack surveys of bridge decks, performed over a 10-year period in northeast Kansas as part of three studies, provide strong guidance in identifying the parameters that control cracking in these structures. The surveys involve steel girder bridges—bridges that are generally agreed to exhibit the greatest amount of cracking in the concrete decks. The surveys include monolithic decks and decks with silica fume and conventional concrete overlays. The study demonstrates that crack density increases as a function of cement and water content, and concrete strength. In addition, crack density is higher in the end spans of decks that are integral with the abutments than decks with pin-ended supports. Most cracking occurs early in the life of a bridge deck, but continues to increase over time. This is true for bridges cast in both the 1980s and the 1990s. A key observation, however, is that bridge decks cast in the 1980s exhibit less cracking than those in the 1990s, even with the increase in crack density over time. Changes in materials, primarily cement fineness, and construction procedures over the past 20 years, are discussed in light of these observations. A major bright spot has been the positive effect of efforts to limit early evaporation, suggesting that the early initiation of curing procedures will help reduce cracking in bridge decks.

Strength and Related Properties of Brick Masonry

Sixteen important controllable variables in the strength of conventional brick masonry are related in 10 equations for strength in compression, flexure, and shear. Axial compressive strength of standard brick masonry prisms is a function of the compressive strengths of brick and mortar and quality of workmanship. The compressive strength of brick is a function of unit size and shape, raw material, manufacturing process and degree of burning. Compressive strength of mortar is a function of cement, lime, water and air content, curing condition and batch life. Flexural strength of brick masonry is a function of brick-mortar bond, joint thickness, and mortar cement content. Bond strength of brick to mortar is a function of mortar flow, air content, and exposure time, and brick suction and surface condition. Shear strength of brick masonry is a function of brick-mortar bond strength, compressive stress and coefficient of internal friction.