Durability of Wet Bond of Hybrid Laminates to Cast-in-Place Concrete

Wet bond is a chemical bond developed to connect fiber-reinforced polymer (FRP) stay-in-place formwork to cast-in-place concrete for a composite action. Curing of chemical adhesive and fresh concrete occurs simultaneously in wet bond. Since FRP-concrete composite structure so designed is strongly dependent on the bond between FRP and concrete, a durable bond is of paramount importance. This paper presents a study on durability performance of wet bond exposed to sustained low temperature, freeze-thaw cycles, and wet-dry cycles. Single lap pull-off tests were conducted to evaluate the effect of exposure on bond. It was found that both first crack load and ultimate load of wet bond were reduced in comparison to dry bond. This reduction was more severe in first crack load than in ultimate capacity and was associated with voids, thickness, and surface of adhesive layer. The epoxy in wet bond had reached comparable degree of cure to dry bond and even gained a higher Tg. Environmental exposures did not show more impact on wet bond than on dry bond.     

Investigating a Structural Form System for Concrete Girders Using Commercially Available GFRP Sheet-Pile Sections

This paper presents a new girder consisting of a trapezoidal pultruded glass fiber-reinforced polymer (GFRP) hat-shaped section commercially available as a sheet pile, but used in this study as a structural form for concrete. It can also offer continuity in the transverse direction through a pin-and-eye connection. Five 610?mm×325?mm and 3,300-mm-long girders were tested in flexure to examine different bond systems, voided and solid concrete cores, and the performance in positive and negative bending. Bond systems were wet adhesive bond to freshly cast concrete, adhesively bonded coarse aggregates, and mechanical shear studs. No slip was observed between concrete and the GFRP section until delamination failure occurred within a thin layer of cement mortar that remained attached to GFRP. The studs failed by pull out from the concrete flange. In general, 47–75% of the full strengths of concrete and GFRP were reached at ultimate bond failure. Wet adhesive bonding was the simplest and quickest to apply, while resulting in a comparable strength to other systems. A “moment-curvature” analytical model, incorporating a robust bond failure criterion, was developed, validated, and used in a parametric study. It showed that varying the concrete compressive strength or thickness of the GFRP section has insignificant effect on the bond failure load. Also, there are critical values for shear span-to-depth ratio, shear strength of cement mortar, concrete strength, and width of the top GFRP flange, beyond which, the desired flexural failure mode would precede bond failure.     

Thrombotic microangiopathy after liver-small bowel transplant

We herein report the first case of immunosuppression-associated thrombotic microangiopathy (TMA) in which an extrarenal graft was primarily affected by the characteristic microvascular lesions. Although TMA is a well-known complication of cyclosporine (CSA) or tacrolimus therapy in renal and extrarenal (liver, heart, lung) transplant recipients, the kidney (transplanted or native) is typically the site primarily affected. We describe a combined liver-small bowel transplant recipient who developed tacrolimus-associated TMA that affected both her transplanted small bowel and her native kidneys. Involvement of the bowel, with evidence of microvascular occlusion on biopsy, led to the development of ischemic mucosal ulcers and eventual bowel perforation. Involvement of the kidney manifested with a doubling of the recipient's baseline serum creatinine level. Significant lowering of the tacrolimus dose resulted in healing of the small bowel ulcers and return to her baseline level of renal function. Therefore, it is important to note that, in transplant recipients, TMA with microvascular occlusion may affect extrarenal sites. In small bowel transplant recipients, the result might be ischemic ulcers in the graft and eventual bowel perforation.     

Calculation of Moisture Distribution in Early-Age Concrete

The moisture content in concrete pores is a critical parameter for most of the degradation processes suffered by concrete, such as concrete shrinkage and related cracking. The objective of this paper is to present the formulation of a general moisture distribution model for young-age concrete. In the modeling, both cement hydration and moisture diffusion resulted humidity variations are taken into account synchronously. The effect of initial water distribution (after concrete casting) on the development of moisture distribution is considered by introducing a critical time parameter. The simulation of humidity reduction produced from self-desiccation is based on cement hydration degree that taking the effect of temperature into account by using the equilibrant age concept. During modeling the moisture diffusion, a multilinear model was adopted to simulate the moisture dependent diffusivity. The developed model and finite deferential method can well predict the moisture distribution as well as its variations with time. Good agreement between model predictions and experimental results is found. These results can subsequently be used in shrinkage induced stress field analyses, and further be used for cracking control of concrete structures.     

Water Migration Phenomenon Model in Cracked Concrete.?I: Formulation

A mathematical model for water migration in concrete that changes from a homogeneous to a nonhomogeneous material due to its loading history is developed in detail. In the proposed model, concrete is assumed to be composed of aggregate, cement paste, water, a crack band, and an interfacial crack between the aggregate and cement paste. The discontinuities for displacement and hydraulic gradient on cracks are considered on the microlevel. Then the governing equation for water migration in concrete as a homogeneous and a nonhomogeneous material is developed by coupling the mass conservation law and the force equilibrium. Therefore, it is possible to apply the developed model not only to cement-based material but also to porous permeable material like soil material and rock. However, the applicability of the developed model must be confirmed by comparing the experimental results.     

Construction Quality Control for Asphalt Concrete Hydraulic Barriers

Asphalt concrete has been used for low permeability barriers in numerous applications over many centuries. In recent times, asphalt concrete barriers have been used for waste containment applications. The hydraulic conductivity of asphalt concrete specimens can be measured in the laboratory; however, there is no expedient, efficient way of accurately measuring the in situ hydraulic conductivity of low permeability asphalt concrete shortly after its placement and compaction in the field. A method has been developed to efficiently check the in situ hydraulic conductivity of asphalt concrete in the field. Asphalt concrete specimens with varying asphalt cement contents and unit weights were prepared in the laboratory and their hydraulic conductivity measured. The measured hydraulic conductivity data were grouped into different ranges and plotted as a function of unit weight and asphalt cement content. An acceptable zone was specified for a combination of asphalt cement content and unit weight that resulted in a specified hydraulic conductivity. In the field, a quality control inspector can check the unit weight and asphalt cement content of the in-place barrier to make sure it lies within the acceptable zone. The asphalt cement content and unit weight can be readily measured, thereby allowing rapid acceptance or rejection of the asphalt concrete barrier shortly after compaction.     

Modeling of Water Migration Phenomenon in Concrete as Homogeneous Material

A mathematical model for water migration in concrete as a homogeneous material (one that does not contain cracks) is developed in detail. In the proposed model, concrete is assumed to be composed of aggregate, cement paste, and water, for which the compressibility is taken into account. Then, the governing equation for water migration in concrete as a homogeneous material is developed by coupling the mass conservation law and the force equilibrium equation.     

Assessing the Efficiency of CFRP Discrete Confinement Systems for Concrete Cylinders

Concrete columns requiring strengthening intervention always contain a certain percentage of steel hoops. Applying strips of wet layup carbon fiber-reinforced polymer (CFRP) sheets inbetween the existent steel hoops might, therefore, be an appropriate confinement technique with both technical and economic advantages, when full wrapping of a concrete column is taken as a basis of comparison. To assess the effectiveness of this discrete confinement strategy, circular cross-sectional concrete elements confined by distinct arrangements of strips of CFRP sheet are submitted to a direct compression load up to the failure point. The influence of the width of the strip, distance between strips, number of CFRP layers per strip, CFRP stiffness, and concrete strength class on the increase of the load carrying capacity and ductility of concrete columns, is evaluated. An analytical model is developed to predict the compressive stress-strain relationship of concrete columns confined by discrete and continuous CFRP arrangements. The main results of the experimental program are presented and analyzed and used to assess the model performance.     

水泥砼旧路面加铺沥青砼路面层中防反射裂缝的主要措施简析

水泥混凝土路面是我国城市道路的主要类型，在旧水泥混凝土路面上加铺沥青混凝土面层是改善路面使用性能、提高路面使用寿命的主要措施之一。本文简要分析了反射裂缝产生的机理，以及各主要技术措施能防止或延缓反射裂缝的机理。     

Cost-minimization analysis of intravenous adenosine and dipyridamole in thallous chloride TI 201 SPECT myocardial perfusion imaging

This paper deals with two patients with acetaminophen-induced pneumonitis. A 64-year-old woman suffered from mastitis while being treated by corticosteroid therapy for phemphigoid. She was administered antibiotics and acetaminophen. However, her fever continued and she subsequently developed dyspnea and interstitial pneumonia. The other patient, a 70-year-old woman, was treated with corticosteroid for lower motor neuron disease. Anti-GM1-IgM antibodies were positive in her serum. She developed wet cough and mild fever. During treatment with antibiotics and acetaminophen, her illness was complicated by dyspnea and interstital pneumonia. As a result of histological findings of transbronchial lung biopsy specimens showing interstitial infiltration of mononuclear cells, as well as clinical courses in which cessation of acetaminophen directly lead to the improvement of interstitial pneumonia, both patients were diagnosed to have acetaminophen-induced pneumonitis. The peumonitis responded well to steroid therapy. In vitro culture of peripheral lymphocytes showed stimulated proliferation by acetaminophen in both patients. These findings suggest that allergic mechanism was involved in the pathogenesis of the pneumonitis. Underlying immunological disorders may have enhanced the occurrence. Although acetaminophen is one of the most popular drugs because of a very low incidence of side effects, this drug should be applied carefully, especially with patients who have such immunological disorders.     

Lessons from Roman Cement and Concrete

Although masonry and lime mortars had been used for centuries by earlier civilizations, the Romans were the first to extensively use naturally occurring volcanic earth to make hydraulic cement. The volcanic powder named “pulvis puteolanis,” found near the town of Puteoli near Naples (now Pozzouli), was used to build magnificent structures. The use of this hydraulic cement in masonry and concrete greatly expanded civil engineering possibilities. The Roman engineer Vitruvius, writing in The Ten Books on Architecture, described the careful materials selection, proportioning, and workmanship that was critical to the performance of Roman concrete. Masonry and coarse and fine aggregates were carefully selected for durability. Hydraulic cement concrete was used extensively for constructing bridge piers and harbor jetties. One of the greatest examples of Roman concrete construction was the dome of the Pantheon, with its 43.4-m span. The vast system of aqueducts also made extensive use of hydraulic cement. This paper summarizes the materials and construction methods used in Roman concrete construction, as well as structures and infrastructure built with concrete.     

如何预防水泥混凝土路面的裂缝和断板

介绍了水泥混凝土路面几种常见裂缝类型,并进行了简要的原因分析,提出了预防水泥混凝土路面裂缝(或断板)的措施。     

Corrosion Condition Evaluation at Muddy Creek Bridge

Corrosion rates were measured at the exposed spots of rebars near three corners of Muddy Creek Bridge located in northern West Virginia using a 3LP device. Also, chloride contents of the concrete samples taken from the vicinity of the spots were analyzed using a wet chemical method that had been developed in this study. The average corrosion rate over the three spots was 4.66 mA/m2, which is in the range of corrosion damage possible in 10–15 years. The average chloride content of the concrete over the three spots was 703 parts per million (ppm), which is well above the threshold limit value of 260 ppm. Although the corrosion rate measurement method using a 3LP device is by manual operation, it is found to be reliable and effective, and, thus, recommended for future studies of this kind of research. The wet chemical method developed in this study is found to be effective.     

Laboratory Testing Material Property and FE Modeling Structural Response of PAM-Modified Concrete Overlay on Bridges

Portland cement concrete overlay on bridge deck is subjected to distresses of cracking and interface debonding under the effects of repeated vehicle loading and temperature cycling. In order to improve the overlay performance, this research used the polyacrylamide (PAM) polymer to modify the mechanical properties of concrete. The direct shear and impact resistance tests were designed to measure the interface bonding strength and dynamic performance, respectively. The comprehensive and flexural strength and three-point bending fatigue tests were conducted following the standards. Meanwhile, the three-dimensional finite-element (FE) models of the T-girder and box-girder bridges under the moving traffic loadings were built to analyze the stress response and improve the structural design. An analytical model of flexural stress was developed and validated the FE modeling results. A rubber cushion was designed in the FE model to “absorb” the flexural stress. Laboratory testing results indicate that PAM can significantly improve the flexural strength, bonding strength, impact resistance, and fatigue life of concrete. The modified concrete with 8% PAM by mass of cement poses higher flexural strength and impact resistance than concretes with other PAM percentages. FE simulation results indicate that there exists a critical overlay thickness inducing the maximum interface shear stress, which should be avoided in the structural design. The rubber cushion can effectively relieve the flexural stress.     

Wet cement: a poorly recognized cause of full-thickness skin burns

Cement is a rare cause of full-thickness burns. We have examined the aetiology, frequency and severity of these burns, and assessed public awareness of the potential of cement as a caustic agent. Of patients, 95 per cent were unaware of the potential of cement to cause burns, and none had seen precautionary warnings on cement bags or delivery dockets. Factors important in burn production appear to be alkalinity, duration of contact and the abrasive nature of the cement particles. It is concluded that doctors, especially casualty officers, should know of the potential of progressive full-thickness burns from wet cement. General public awareness should be increased. The cement manufacturers were asked to comment on the content of this paper.     

Prediction Models for Debonding Failure Loads of Carbon Fiber Reinforced Polymer Retrofitted Reinforced Concrete Beams

This study focuses on debonding failure in reinforced concrete beams with carbon fiber reinforced polymer composite bonded on the soffit using the wet lay-up method. An experimental study, which involved 26 tests, was carried out. The experiments showed two failure modes: Intermediate span debond and end debond. The first failure is the result of the high bond stress near the tip of a flexure-shear crack, whereas the second type of failure is due to the high shear stress developed in the weakest concrete layer at the tension reinforcement level. The experiments have shown that U-straps can be effective in preventing intermediate span and end debond. Based on experimental observations, two simple and practical theoretical models were developed and verified with the experimental data, together with a large database of other existing tests.     

Confinement of Damaged and Nondamaged Structural Concrete with FRP and TRC Sleeves

The potential for using textiles impregnated with cement as a means for in situ strengthening and retrofit of structural concrete was explored and compared with the conventional epoxy method. Fabrics of different geometries, yarns, and modulus values were evaluated. Simulation of repair and strengthening was carried out by wrapping fabric impregnated with cement and epoxy around damaged and undamaged concrete cylinders. The cylinders with the impregnated sleeves were loaded in compression, and their performance was compared with that of the “virgin” (control) concrete. In addition, the mechanical properties of the cement composite layer were evaluated, as well as the stiffness of the fabrics themselves, and correlated with that of the repaired system. Efficient repair with the cement binder was accomplished with the high modulus fabric (Kevlar) in particular. However, even the lower modulus (polypropylene) could be effective in repairing and inducing some postpeak resistance (although to a smaller extent than with the Kevlar). Improved behavior was also obtained with the nondamaged concrete cylinder when it was strengthened with the cement–fabric jacket, mainly at composite strain values of up to 0.2–0.3%.     

Modeling Water and Sulfuric Acid Transport through Coated Cement Concrete

The behavior of coated cement concrete in water and sulfuric acid was investigated over a three-year period. Two epoxy-based coatings were selected and cylindrical concrete specimens were coated and used in this investigation. The concrete-to-coating mass transfer coefficient ratio varied from 8 to 10. The penetration of liquids through bulk coating materials and coated concrete with and without holidays (pinholes) was studied. The mass change of the specimens was measured at regular intervals and a total of 64 coated specimens were tested. Coated concrete specimens with and without holidays had different performance with long-term immersion in deionized (DI) water and 3% sulfuric acid. Mass transfer models were developed using film and bulk concepts and were used to predict the increase in mass in coated concrete in nonreactive DI water and reactive 3% sulfuric acid solutions. The mass transfer model parameters for various solution-coating combinations were obtained from experiment data. The parameters of the effect of holiday size on the liquid transport process were also identified based on the experiment results.     

Evaluation of Calcofluor staining in the diagnosis of fungal corneal ulcer

For laboratory diagnosis of mycotic keratitis, demonstration of fungal pathogens on direct microscopy and their isolation by culture is essential. The addition of Calcofluor white (CFW) stain to the diagnostic armamentarium has significantly increased the sensitivity of smear examination on direct microscopy. During a period of 1 year, 143 consecutive patients with corneal ulcers were investigated by direct microscopy with potassium hydroxide (KOH) wet mount, Calcofluor white stain and routine cultures of corneal scrapings. Fungi were detected as aetiological agents in 21 (15%) patients. Different species of the genera Aspergillus (35%), Fusarium (23%), Acremonium (12%), Paecilomyces (12%), Cladosporium (6%), Alternaria (6%) and Pseudallescheria (6%) were the common isolates. Calcofluor white stain on direct microscopy detected fungi in 20 (95.2%) patients in comparison with 15 (71.4%) patients by both KOH wet mount examination and culture. Calcofluor white stain was significantly more sensitive than KOH wet mount in demonstrating fungal pathogens.     

Microstructural Mechanisms of Early Age Cracking Behavior of Concrete: Fracture Energy Approach

This paper presents findings from a study directed at identifying key properties of ingredient materials that are influential on the early age cracking behavior of concrete, with an emphasis on the effects of aggregate size, aggregate morphologies, and water-cement ratio (w/c). Fracture energy (GF) was determined using a wedge-split test configuration for concrete samples at the age of 12?h. Based on image analysis, three signature morphologies of aggregate particles, i.e., the angularity, surface texture, and surface area, were quantitatively determined in terms of developed angularity index (AI), surface texture (ST) index, and surface area (SA) measurement, respectively. The high consistency between GF and aggregate SA of the concrete samples suggests that the interfacial transition zone (ITZ) at the cement paste-aggregate interface is the critical location that primarily accommodates the 12?h cracking of concrete. The critical role of ITZ in the early age cracking of concrete was further confirmed by its microstructural and chemical features under scanning electron microscopy/energy dispersive X-ray spectroscopy.