Microstructural Evaluation of Durability of Different Cementitious Mixtures in Microbial Induced Corrosion Environments

Sound and durable concrete mixtures are essential in environments where microbial induced corrosion (MIC) is a concern. In this study three concrete mixtures prepared with different binders (ordinary portland cement (OPC), calcium aluminate cement (CAC) and alkali-activated cement (AAC) were petrographically examined after exposure to laboratory-controlled MIC conditions. Analytical techniques included reflected light microscopy, polarized and fluorescent transmitted light microscopy (FLM) and scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer (SEM/EDX). SEM/EDX analyses obtained from the same areas provided information on chemical and mineralogical alteration, while quantitative image analysis with FLM affords an opportunity to quantify the variation in capillary porosity of the paste within alteration zonation. The microscopic observations indicate that the change in normalized capillary porosity coincide broadly with different alteration zones, which are in turn dependent on the type of binder. The OPC concrete shows the greatest deterioration where the paste is largely replaced by gypsum and high capillary porosity is lined to leaching of a calcium. The formation of ettringite densifies the paste and lowers the capillary porosity inboard of the gypsum zone in the OPC concrete. The CAC and AAC mixtures show better resistance to leaching than the OPC mixture, which explains their superior resistance to MIC. These findings are consistent with independent macroscopic observations that indicate the OPC mixture deteriorated more rapidly and severely than the CAC and AAC mixtures

Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor

The durability of in-place concrete is a high priority issue for concrete pavements and bridges. Several studies have been conducted by INDOT to use electrical resistivity as a measure of fluid transport properties. Resistivity is dependent on the chemistry of the cement and supplementary cementitious system used, as such it has been recommended that rather than specifying resistivity it may be more general to specify the formation factor. Samples were tested to establish the current levels of performance for concrete pavements in the state of Indiana. Temperature and moisture corrections are presented and acceptable accelerated aging procedure is presented. A standardized testing procedure was developed (AASHTO TP 119–Option A) resulting in part from this study that provides specific sample conditioning approaches to address pore solution composition, moisture conditioning, and testing procedures. An accelerated aging procedure is discussed to obtain later age properties (91 days) after only 28 days

Synthesis: Accelerating Implementation of Research Findings to Reduce Potential Concrete Pavement Joint Deterioration

Distress has recently been observed in the joints of some concrete pavements, primarily in the wet-freeze states. This distress often begins in longitudinal joints, followed by transverse joints and results in the significant loss of material from the joint area. Although it may only affect approximately 10% of the concrete pavements system-wide, it greatly reduces the service life and increases maintenance costs of the pavements it effects. Primary issues that emerged from studies on this phenomenon include the importance of the timing of joint sawing, the width of the joint opening, degree of concrete or joint sealing, drainage and degree of saturation of the concrete at the joint, quality of the air void system, role of deicing chemicals, quality of curing, and the degree of restraint at the joint. Although this broad collection of issues implies that we still lack complete understanding of all causes of joint deterioration, it also makes it pretty clear that the observed damage is a result of combination of several factors. This study synthesizes completed research related to concrete pavements joint deterioration and provides information to advance the knowledge and understanding of the variables involved in in this deterioration process and suggests the best practices that can lead to its reduction or mitigation

Metformin promotes the survival of transplanted cardiosphere-derived cells thereby enhancing their therapeutic effect against myocardial infarction

The CDC differentiation at 4 weeks after transplantation analyzed by immunostaining. A–C: Sections of hearts were immunostained with antibodies to (A) the cardiomyocyte marker tropomyosin, (B) the endothelial cell marker von-Willebrand Factor (vWF), and (C) the smooth muscle cell marker α-smooth muscle actin (α-SMA). Antibody to GFP was used for identifying surviving CDC-derived cells and DAPI was used for identifying nuclei. Scale bars = 20 μm. DAPI 4′,6-diamidino-2-phenylindole. (PDF 178 kb

Latitudinal patterns of forest ecosystem stability across spatial scales as affected by biodiversity and environmental heterogeneity

Our planet is facing a variety of serious threats from climate change that are unfolding unevenly across the globe. Uncovering the spatial patterns of ecosystem stability is important for predicting the responses of ecological processes and biodiversity patterns to climate change. However, the understanding of the latitudinal pattern of ecosystem stability across scales and of the underlying ecological drivers is still very limited. Accordingly, this study examines the latitudinal patterns of ecosystem stability at the local and regional spatial scale using a natural assembly of forest metacommunities that are distributed over a large temperate forest region, considering a range of potential environmental drivers. We found that the stability of regional communities (regional stability) and asynchronous dynamics among local communities (spatial asynchrony) both decreased with increasing latitude, whereas the stability of local communities (local stability) did not. We tested a series of hypotheses that potentially drive the spatial patterns of ecosystem stability, and found that although the ecological drivers of biodiversity, climatic history, resource conditions, climatic stability, and environmental heterogeneity varied with latitude, latitudinal patterns of ecosystem stability at multiple scales were affected by biodiversity and environmental heterogeneity. In particular, α diversity is positively associated with local stability, while β diversity is positively associated with spatial asynchrony, although both relationships are weak. Our study provides the first evidence that latitudinal patterns of the temporal stability of naturally assembled forest metacommunities across scales are driven by biodiversity and environmental heterogeneity. Our findings suggest that the preservation of plant biodiversity within and between forest communities and the maintenance of heterogeneous landscapes can be crucial to buffer forest ecosystems at higher latitudes from the faster and more intense negative impacts of climate change in the future

LKB1 suppression promotes cardiomyocyte regeneration via LKB1-AMPK-YAP axis

The regenerative potential of cardiomyocytes in adult mammals is limited. Previous studies reported that cardiomyocyte proliferation is suppressed by AMP-activated protein kinase (AMPK). The role of liver kinase B1 (LKB1), as the major upstream kinase for AMPK, on cardiomyocyte proliferation is unclear. In this study, we found that the LKB1 levels rapidly increased after birth. With loss- and gain-of-function study, our data demonstrated that LKB1 levels negatively correlate with cardiomyocyte proliferation. We next identified Yes-associated protein (YAP) as the downstream effector of LKB1 using high-throughput RNA sequencing. Our results also demonstrated that AMPK plays an essential role in Lkb1 knockdown-induced cardiomyocyte proliferation. Importantly, deactivated AMPK abolished the LKB1-mediated regulation of YAP nuclear translocation and cardiomyocyte proliferation. Thus, our findings suggested the role of LKB1-AMPK-YAP axis during cardiomyocyte proliferation, which could be used as a potential target for inducing cardiac regeneration after injury

Phase Diagram and Volume Change of the Ca(OH)2─ CaCl2─ H2O System for Varying Ca(OH)2/CaCl2 Molar Ratios

AbstractCalcium chloride (CaCl2) from deicing salts can react chemically with calcium hydroxide [Ca(OH)2] from hydrated cement paste to form an expansive product, calcium oxychloride, that can damage concrete. This paper uses two experimental techniques, volume change measurement and low temperature differential scanning calorimetry (LT-DSC), to characterize the phase transitions associated with the formation of calcium oxychloride in the Ca(OH)2─ CaCl2─ H2O system. The temperature at which calcium oxychloride begins to form increases as the CaCl2 concentration increases, and it is not influenced by the [Ca(OH)2/CaCl2] molar ratio. Within the testing temperature range, the extent of reaction [the mass percentage of Ca(OH)2 consumed to form calcium oxychloride] increases as the CaCl2 concentration increases; the extent of reaction decreases as the [Ca(OH)2/CaCl2] molar ratio increases. The temperatures associated with the phase transitions are used to develop phase isopleths for the Ca(OH)2─ CaCl2─ H2O system for varying concentrations and molar ratios. These phase isopleths are integrated to form a ternary phase diagram of the Ca(OH)2─ CaCl2─ H2O system. The phase diagram provides a powerful tool to determine the phase transitions in the Ca(OH)2─ CaCl2─ H2O system as the [Ca(OH)2/CaCl2] molar ratio varies

Flexural strength reduction of cement pastes exposed to CaCl2 solutions

Calcium chloride (CaCl2) can react with calcium hydroxide (Ca(OH)2) to form calcium oxychloride which can reduce flexural strength and damage concrete. This paper aims to characterize the reduction in flexural strength of cement pastes exposed to CaCl2 solutions using the ball-on-three-balls test. The amounts of Ca(OH)2 and calcium oxychloride in the cement paste are measured using thermogravimetric analysis and low-temperature differential scanning calorimetry, respectively. The volume change that occurs as a result of the reactions between the cement paste and CaCl2 is also measured. The reduction in flexural strength increases as the concentration of the CaCl2 solution increases and the exposure temperature decreases. The flexural strength reduction can be mitigated by increasing the amount of supplementary cementitious materials (fly ash) in the cement pastes. Lowering the water-cementitious materials ratio also reduces the flexural strength reduction. The flexural strength reduction is correlated with the amount of calcium oxychloride and the volume change in the cement pastes exposed to the CaCl2 solution. While the flexural strength reduction is believed to be primarily due to the formation of calcium oxychloride, the formation of Friedel's salt and Kuzel's salt also contributes to the flexural strength reduction