Total Crack Area Research Articles

Porewater salinity effect on flocculation and desiccation cracking behaviour of kaolin and bentonite considering working condition

Cracking behaviour of clays at a local working climate and soils' evolution under seepage boundary is very important for the geological engineering. In coastal regions, pore water salinity is incorporated into above processes. In this study, the properties of typical clays (kaolin and bentonite) in saline environments, including the consistency limits, particle sedimentation and crack pattern, were investigated. The consistency limits of kaolin remain constant regardless of the pore water salinity, while the liquid limits of bentonite noticeably decrease with increasing salinity. Flocculation of kaolin occurs in both distilled water and NaCl solution, whereas the fine particles in bentonite disperse in distilled water but aggregate in saline water. At the end of the evaporation process, the total crack area of bentonite is obviously decreased, and the total crack length increases with pore water salinity, whilst that of kaolin is not influenced. In the subsequent wetting process, the bentonite clods disperse easily in saline environment, but the collapse of kaolin clods is not significantly influenced by the water salinity. The above observations are explained by the initial aggregation of clay platelets for the interactive forces between particles.

Effect of nano-SiO2 on strength, shrinkage and cracking sensitivity of lightweight aggregate concrete

This paper presents an experimental investigation on the effect of nano-SiO2 on the compressive strength, shrinkage and early cracking sensitivity of lightweight aggregate concrete (LWAC). Two types of ceramsite with different water absorption were used as lightweight aggregate in this study. LWAC with different nano-SiO2 dosage (1%, 2%, 3%) were compared with the reference LWAC to assess the effects of nano-SiO2 on LWAC. Results revealed that the incorporation of 3% nano-SiO2 increased compressive strength of LWAC significantly while the influence of nano-SiO2 on the long-term shrinkage of LWAC was not significant. The total cracking area was decreased with the increase in nano-SiO2 dosages from 1% to 3% by mass of the total binders at early age. The results of scanning electron microscopy (SEM) showed that the interfacial transition zone (ITZ) between lightweight aggregate and paste was enhanced with 3% nano-SiO2 addition. Subsequently, simplified models for compressive strength and shrinkage of LWAC were proposed and a comparison between the experimental data and models was discussed.

Pavement Condition Assessment Using IRI from Roadroid and Surface Distress Index Method on National Road in Sumenep Regency

The pavement condition will decrease due to the influence of traffic and environment, so that the maintenance effort is needed to maintain the road condition during the service period. In order to carry out road maintenance activities right on target, there needs to be a plan based on accurate pavement condition data. Road roughness is the most commonly used condition parameter in evaluating pavement conditions objectively because road roughness data is relatively easy to obtain, well correlated with vehicle operating costs and the most relevant parameter in road functional performance measurement. The Roadroid is an Android-based application that measures road roughness by using vibration sensors on a smartphone so it is possible to get an International Roughness Index (IRI) value as an indicator of pavement conditions more easily and efficiently. Besides based on road roughness, pavement condition evaluation can also be done visually by using Surface Distress Index (SDI) method that uses the total crack area parameters, average crack width, total number of potholes and the average depth of rutting. This study attempts to assess the condition of Jenderal Sudirman-Kalianget road by combining IRI Roadroid value and SDI value which will be used as the basis to determine the required road maintenance. This road segment is one of the national strategic road connecting the center of Sumenep regency with the Kalianget harbor. Based on IRI measurement and SDI calculation, the pavement condition of Jenderal Sudirman-Kalianget road can be described 4.2 kilometers (37.17%) were good and 2.3 kilometers (20.35%) were fair that need routine maintenance. While 2.1 kilometers (18.58%) were bad and 2.7 kilometers (23.89%) were poor that need periodical maintenance and reconstruction.

Cold Roll Bond of Al-St Strips with Wire Brush Surface Treatment

The effect of interface microstructure by wire brush treatment on the bond strength of Al-St clad strips by cold roll bonding was investigated. For the purpose, wire brush surface preparations on steel strip surface have been done before the cold roll bonding of the Al-St clad strips, and evaluate the sample bonding strength by peeling test of the rolling deformation zone. The results show that bond strength of Al-St strip by wire brush treatment increases with the total reduction increases and the threshold reduction of Al-St strip is 15%. Meanwhile the total crack area increase with the reduction. The oxide film on the surface of brittle layer hinds the metal bond and the crack between the scratch brush layer and substrate metal is the weak point and decrease the bond strength. A major feature of the bonding mechanism described in this paper is that extruded aluminum squeezed into the cracks of steel surface by normal roll pressure action, and metallic bond with underlying fresh steel metal.

Influence of magnetic water on early-age shrinkage cracking of concrete

This research investigates the shrinkage cracking of concrete, which were mixed with magnetic water. Magnetic water was obtained by the independent designed magnetizing equipment. Ring-test method and flat-test method were used to test early-age shrinkage cracking of concrete. Results show that the strain rate factor (α) and the total cracking area of unit area (c) of concrete were decreased when used magnetic water, which means the early-age shrinkage cracking resistance of concrete mixed with magnetic water is improved than those mixed with tap water. The best increase in early-age shrinkage cracking resistance of concrete is achieved when the magnetic strength is 260mT and the length of magnetic field is 280mm. Additionally, the compressive and split strength of concrete mixed with magnetic water increased greatly. It is also found that the length of magnetic field have direct effect on the growth of concrete strength.

Effect of Mineral Admixture and Fibers on Shrinkage Crack of Sacrificial Concrete

The ferro-siliceous sacrificial concrete is an important protection material to Nuclear power plant, high density aggregate and high fluidity can lead to occurrence of shrinkage crack. In this paper, the early-age crack and restrained shrinkage crack of sixteen types of sacrificial concrete containing different content of cementitious materials and two kinds of fibers were researched. Results showed that the workability of sacrificial concrete decreased with increasing addition of fiber, and the slump loss resulted from polypropylene (PP) fiber was much higher than that of basalt fiber. The fibers had less influence on the compressive strength, while had greater impact on the flexural strength, which was improved by 10-20%. The reduction of total cementitious materials and replacement ratio increment of mineral admixtures including fly ash and Ground Granulated Blastfurnace Slag (GGBS) in sacrificial concrete could decrease its early-age crack obviously. The utilization of 1.0-1.5kg/m(3) PP fiber could extend the cracking time and reduce the crack width of sacrificial concrete and total cracking area. The improving crack resistance capacity of sacrificial concrete resulted by basalt fiber was weaker than PP fiber. The optimized mix proportion of sacrificial concrete mixture was 450kg/m(3) total cementitious materials, 50% replacement ration of mineral admixtures and 1.0kg/m(3) PP fiber.

Comparative study between natural and PVA fibers to reduce plastic shrinkage cracking in cement-based composite

The main objective of this study is to control restrained plastic shrinkage cracking through the addition of natural and PVA fibers in a cement-based composite. Two types of natural fibers (flax and agave lechuguilla) as well as synthetic fibers (PVA) were investigated at volume fractions of 0.1% and 0.7%. 38 prismatic mortar specimens were freshly cast on top of a grooved and hard concrete substrate, providing a bottom restraint; this resulted in cracking in the freshly placed overlay, which was detected as a function of time. The effectiveness of the fibers was evaluated by considering reducing the number of cracks and total crack area under these conditions. The results obtained show that both natural fibers were effective in controlling restrained plastic shrinkage cracking like the commercially available PVA fibers; the total crack areas were also reduced by at least 93% compared with plain mortar specimens.

Correlating plastic shrinkage cracking potential of fiber reinforced cement composites with its early-age constitutive response in tension

It is well understood that the early-age properties of cementitious materials influences its long-term performance. Cementitious materials experience high moisture loss at early age resulting in volumetric shrinkage. When this shrinkage is restrained, tensile stresses develop resulting in cracking of the material. This issue is more pronounced at early-age when the tensile strength of cementitious materials is not fully developed. There are many methods and models available to predict the drying shrinkage of concrete. However, the relationship between early age uniaxial tensile strength and restrained shrinkage cracking characteristics at early age is not well understood. Uniaxial tests were conducted on dog-bone specimens made using various fiber types including glass, cellulose and three types of synthetic fibers. Tensile characteristics including stress versus strain plots for all the specimens along with stress at peak, post crack strength at 2 mm deflection along with elongation at peak are calculated and presented in this paper. Plastic shrinkage cracking results obtained using an innovative test developed by the authors were correlated to these tensile strength results. Results indicate that post crack residual tensile strength at early-age is inversely proportional to the total crack area resulting from restrained shrinkage. The effectiveness of various fiber types is also discussed in the paper.

EFFECT OF WATER SOLUBLE POLYMER AND FIBER ON THE EARLY-AGE SHRINKAGE CRACKING OF CEMENTITIOUS COMPOSITES

Both polymeric fiber and water soluble polymer (WSP) have been reported effective in reducing early-age shrinkage cracking. The synergistic effect of cellulose based WSP and fiber on reducing early-age shrinkage cracking of cementitious composite exposed to a constant evaporation rate of 1 kg/(h.m2) environment was investigated in this paper. A fixed ratio of WSP was employed in the poly-acrylic fiber reinforced cementitious composites with various fiber content and aspect ratios. Results indicate that the addition of polymeric fibers reduced plastic shrinkage cracking, such as the total crack area, the average crack width and cracks wider than 1.5 mm. Further reductions on both the crack width and the total crack area were achieved when WSP was used in combination with fibers with an aspect ratio of less than 420. The synergistic reduction on the early-age shrinkage cracking may be attributed to the improvement of the fiber-matrix bond strength and polymer film formation on the drying front. Nevertheless, when fibers with an aspect ratio greater than 420 the synergistic effect provided by the WSP might be masked by the decreased fiber spacing or stronger crackbridging capability. In practical terms, preventing early-age shrinkage cracking by adding WSP not only can reduce fiber requirement but may also keep mixture workable.

The Influence of Polypropylene Fiber on the Performance of Concrete Pavement

This paper presents the influence of the appropriate polypropylene fibers on the performance of cement concrete pavement. The experimental results show that the fibers can obviously reduce cracks and improve the mechanical performance and durability of concrete. When the content of polypropylene fiber is 0.8 kg/m3, the time of the first crack appearance is 45min and 2h 17min later than that of the concrete samples with 0.4 kg/m3 polypropylene fiber and plain concrete. Comparing with the concrete samples with 0.4 kg/m3 polypropylene fiber and plain concrete, the indexes of average crack area, numbers of cracks per area, and total crack area per area of concrete with 0.8 kg/m3 polypropylene fiber reduce 16.2%, 33.0%, 44.3% and 26.9%, 48.1%, 62.2% respectively. Comparing with plain concrete, the 7d and 28d compressive strength of concrete with 0.4 kg/m3 and 0.8 kg/m3 polypropylene fiber enhances 3%, 4% and 4%, 2%, the 90d tensile splitting strength enhances 7% and 10%, and the impact resistance performance of concrete enhances 130% and 250% respectively.

Study on Shrinkage and Cracking Performance of SAP-Modified Concrete

SAPs (Super Absorbent Polymers) are a group of polymeric materials that have the ability to absorb a significant amount of liquid many times their own weight from the surroundings and to retain the liquid within their structure without dissolving and to desorb it in the dry environment. The shrinkage and cracking performance of SAP-modified concrete was studied by experimental investigation, which express as total cracking area from early-age plastic cracking tests and shrinkage rate (restrained and unrestrained) from shrinkage tests respectively. The effect of SAP on shrinkage and cracking of concrete was compared with that of using pre-soaked ceramsite or perlite. The results show that SAP can effectively improve the cracking and shrinkage of concrete with achieving a 30-50% decrease. SAP particles improve the shrinkage and cracking performance of concrete in three ways as absorption-desorption, some absorbed water being bonded with hydrogen bond of macromolecule and filmforming on SAP particles. The coupling effect of SAP retards the water losing and change the moisture distribution in concrete, and thus reducing the cracking and shrinkage of concrete.

Experimental Study on Early Anti-Cracking Properties of Polyvinyl Alcohol Fiber Reinforced Cementitious Composites

This paper mainly studies early anti-cracking of cementitious composites containing polyvinyl alcohol (PVA) fiber and fly ash (FA). The PVA fibers were added at the volume fractions of 0%, 0.25%, 0.5%, 1.0% and 2.0%. The percentages of FA used in the experiment were 0% and 15%. Experimental results show that the maximum crack width and total crack area can be reduced with the increase of volume fraction of PVA fiber, and that no crack appeared at the volume fraction of 2.0%. The reducing tendency of crack width and total crack area kept constant with addition of FA, but reducing amplitude decreased. When the PVA fiber volume fraction remains constant, the early anti-cracking properties of cementitious composites containing PVA fiber and common cement are superior to one containing PVA fiber and FA. Conclusions can be drawn that the early anti-cracking properties of cementitious composites can be improved by PVA fiber.

Effect of viscosity modifying agent on plastic shrinkage cracking of cementitious composites

The effect of cellulose-based viscosity modifying agent (VMA) on plastic shrinkage cracking of cementitious composites exposed to windy environment was examined in this paper. Two molecular weights of VMA with various mixing ratios were employed in the mortar specimens. Plastic shrinkage cracking tests were conducted on a restrained plate subject to a constant evaporation rate of 1,000 g/(m2 h) using a speed adjustable fan in an environmental chamber. Crack pattern, crack width and total crack area were evaluated. In addition, the viscosity of cement paste, surface tension of pore solution, bleeding, and weight changes due to evaporation were also investigated. Addition of VMA affected both surface tension and bleeding, and thereby resulted in the change of evaporation rates and polymer depositions on the drying surface. The cementitious composites with specified VMA doses were found to be very effective in reducing both crack area and crack width and the crack reductions were fairly correlated with surface tension, bleeding and weight changes.

Use of flax fibres to reduce plastic shrinkage cracking in concrete

Abstract An experimental investigation was performed to measure the restrained and unrestrained plastic shrinkage properties of small mortar specimens containing short flax fibres (10–38 mm in length) in amounts ranging from 0.05% to 0.3% by volume. Based on the number of cracks, total crack area, and maximum crack widths produced within the first 24 h after casting and exposure to hot, dry, and windy conditions, flax fibres were found to be slightly more effective in controlling restrained plastic shrinkage cracking than commercially available polypropylene and glass fibres for the mortar mixture studied. At a flax fibre volume fraction of 0.3%, total crack areas were reduced by at least 99.5% relative to plain mortar specimens and maximum crack widths were reduced by at least 98.5% to less than 0.022 mm. Fibre length did not significantly influence cracking behaviour, nor did the presence of flax fibres significantly influence the free plastic shrinkage strains observed.

An Ultrasonic Angle Beam Method for in situ Sizing of Fastener Hole Cracks

Ultrasonic testing is generally recognized as being the preferred nondestructive evaluation (NDE) method for measuring the size of cracks in metals, particularly when access is restricted. Using ultrasonic methods for structural health monitoring imposes the requirement of fixed transducers, which limits the articulation of transducers that is common for NDE. Here we consider the specific problem of in situ sizing of fatigue cracks emanating from fastener holes in aluminum structural components. A dual angle beam through transmission technique is employed whereby the regions of expected crack initiation are interrogated with vertically polarized shear waves. Fatigue cracks partially block the leaky creeping wave spiralling around the hole, and thus reduce the energy of the received signal. The reduction in received energy is directly related to the extent and shape of any open cracks, and this energy is modulated by the applied load as the cracks open and close. The ratio of energy received from the specimen under load to that received under no load is monitored, and this ratio is empirically related to the total crack area. A model is developed to explain this relationship for known crack shapes by assuming an ultrasonic energy profile in the plane of the crack. Data calculated from the model show very good agreement with the experimental results.

Prediction of restrained plastic shrinkage cracking in plain cement concrete

Tests were conducted using specimens that were cast directly on a hardened substrate base as a bonded overlay to simulate restrained plastic shrinkage cracking of concrete. Three concrete mixtures with a fine aggregate/coarse aggregate ratio of unity were tested under four ambient conditions. The test parameters of the study were cement/total aggregate ratio, water/cement ratio and environmental condition. Shrinkage cracking behaviour was studied over a period of 24 h from the time of casting. Partial correlation and multiple regression models based on statistical methodology were developed to predict total crack area induced as a result of plastic shrinkage in Portland cement concrete. The results available in the earlier literature were compared with the results obtained from the model developed. From the results of comparisons the confidence level of the predictive model was found to be more than 95%. This paper reports the test details, the test results, development of the model and the comparisons of test results with the results of the model.

친수성 PVA 섬유보강 시멘트 복합체의 균열제어 및 투수성 평가

초록·키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 실험계획 및 방법3. 실험결과 및 분석4. 결론참고문헌요약

Short fatigue crack parameters describing the lifetime of unnotched steel specimens

The progressive fatigue damage of a material is closely related to the whole population of cracks on the surface of an unnotched specimen. In order to understand which parameter, such as the crack density, the total crack length and the total crack area, is a useful indicator of fatigue damage, rotatory bending fatigue tests are carried out using smooth specimens of medium-carbon steel. The behavior of short crack propagation and the evolution of surface cracks during fatigue are examined. The aim of this paper is to extend the research on fatigue damage in the already studied steel and to study how these damage parameters are correlated with the process of fatigue damage in order to evaluate the effectiveness of damage detection methods.

Investigation into the effect of tillage on solute movement to drains through a heavy clay soil

Abstract. A lysimeter experiment showed a decrease in maximum concentrations and total losses of the herbicide isoproturon leached from a heavy clay soil where the topsoil had a finer, deeper tilth than with a standard agricultural tilth. Volumes of leachate for the first flow event of the season were also smaller and leaching of bromide was slower. The isoproturon was radiolabelled so that its movement could be assessed using a novel radio‐scanning technique. Bypass flow began close to the surface as a scan at 8 cm depth showed that only 0.5% of the total soil area had an activity more than four times the nominal background level. At depths of 10–20 cm, isoproturon was preferentially retained within areas of very fine aggregates. No radioactivity was detected in the scans below 20 cm depth, suggesting little or no retention of isoproturon during transport through the subsoil to the bottom of the lysimeter. Rhodamine‐B dye injected to the base of the topsoil (approximately 20 cm depth) was also used to assess flow pathways through the subsoil. The dye spread laterally across the interface between topsoil and subsoil and then penetrated the subsoil through cracks and fissures. Even within cracks, transport of dye frequently occurred through only a very small proportion of the total crack area. The macropore flow model MACRO 4.0 was used to simulate results from the lysimeter experiment. The fourfold decrease in maximum concentrations of herbicide from the finer tilth lysimeter could be predicted by varying only a parameter describing aggregate sizes at depths of 6–24 cm, suggesting that transfer of herbicide between macropore and micropore regions was faster in the finer tilth. Differences in concentrations of bromide could be simulated only by adjusting the soil hydraulic parameters for the fine tilth to reflect a slight decrease in the predominance of bypass flow relative to matrix flow.

Cracking in recent alluvial soils as related to easily determined soil properties

Cracking was studied in fifty soils located in two recent alluvial plains and it was related to soil parameters such as clay content, soil moisture content, bulk density and coefficient of linear extensibility (COLE). The total crack area per unit soil surface, the crack width and crack depth were measured by tracing them on transparent sheets. The rate of crack development was also studied in a soil immediately after irrigation. Results showed that crack width increased initially almost linearly with decreasing soil moisture content to a certain level and then increased in a declining rate until a maximum width was attained. Cracks appeared on the soil surface after water was removed from the large soil pores. The total crack area occupied a significant portion of the soil surface reaching a maximum value of 22.7%. Measurements of water flow into the cracks during irrigation were significant and in some soils exceeded the conductivity of the uncracked soil surface. An empirical relation was found, which calculates the total crack area per unit soil surface as a function of clay content, COLE and volumetric moisture content. The average crack width was linearly related to the total crack area measured on the soil surface. Furthermore, the crack depth in the plow layer was logarithmically related to clay content, COLE and moisture content.