Influence of Type and Compositions of SCMs on Expansion of Mortar Bars from Alkali Silica Reaction

The effect of different local pozzolans, as a supplementary cementitious material (SCM), on the expansion of mortar bar due to Alkali Silica Reaction (ASR) were reported in this paper. Accelerated test on specimens using local volcanic aggregates, rhyolite, was used to investigate and to compare the effects of fly ash (FA) and metakaolin (MK) on the suppression of the length change. In this study, three different percentages of FA, namely, 20, 35 and 50 and three of MK, namely, 10, 15 and 20 were used in cement replacement. The results showed the lowest expansions at 14 days were -0.036% and -0.001%, respectively for 35% FA and 10% MK, compared to 0.176 % of the control mix. Results from 28 days acceleration registered a slight increase in expansion for both FA and MK mixes.  Increase the SCMs to 50% FA and 15-20% MK yielded reduction of expansion to the innocuous level for both short and long term expansion. Chemical composition analysis revealed decrease in CaO/SiO2 and CaO/Al2O3 of the cementitious systems. This could affect the expansion reduction.  But alumina in Al2O3/SiO2 show the dominant effect on ASR suppression. Microstructures of all materials and casted specimens were also studied in detail. Considering all aspects, these SCMs were considered good candidates for ASR prevention in new concrete structures

Effect of Synthetic and Natural Zeolite on ASR Expansion

The cation exchange capability (CEC), pozzolanic reaction, and filling effects are important keys of natural zeolite for mitigation of Alkali Silica Reaction (ASR), but variation of the zeolite's composition is a major problem when it is utilized. This may not be the case for synthetic zeolite. This paper presents the effects of natural and synthetic zeolite on Alkali Silica Reaction's expansion control. The percentage cement replacement of synthetic and ground natural zeolite-clinotilolite type (SZ and NZ) varied from 0 to 10 and 0 to 20, respectively. It was found that the large percentage replacement (10-20%) changed behaviors of fresh and hardened mixtures significantly. Large replacements of SZ (i.e., 7.5%and 10%) significantly reduced workability and compressive strength, and increased expansion. Slight reductions in expansion were even found for the use of small percentage replacement (SZThe cation exchange capability (CEC), pozzolanic reaction, and filling effects are important keys of natural zeolite for mitigation of Alkali Silica Reaction (ASR), but variation of the zeolite's composition is a major problem when it is utilized. This may not be the case for synthetic zeolite. This paper presents the effects of natural and synthetic zeolite on Alkali Silica Reaction's expansion control. The percentage cement replacement of synthetic and ground natural zeolite-clinotilolite type (SZ and NZ) varied from 0 to 10 and 0 to 20, respectively. It was found that the large percentage replacement (10 - 20%) changed behaviors of fresh and hardened mixtures significantly. Large replacements of SZ (i.e., 7.5% and 10%) significantly reduced workability and compressive strength, and increased expansion. Slight reductions in expansion were even found for the use of small percentage replacement (SZ < 5.0%). Chemical analysis and strength reactivity index tests revealed the non-pozzolanic properties of synthetic zeolite, but not the ground natural zeolite (NZ). The NZ exhibited both pozzolanic reactivity and the capability to significantly reduce expansion. At 20% replacement of NZ, the expansion significantly reduced to none at 14 days of acceleration and less than 0.02% at the longer duration of 28 days. It was confirmed that the high CEC of the studied synthetic zeolite is not the key factor for the effective mitigation for ASR

Early age performance of latex-modified concrete bridge deck overlays

Environmental factors and physical properties of latex modified concrete (LMC) are hypothesized to contribute to early age cracking in bridge deck overlays. Cracking permits the ingress of moisture and aggressive solutions into the substrate and may contribute to other subsequent distresses. Understanding the material properties and mechanisms involved is necessary to minimize these distresses. This research consisted of a two part study: first, the development of LMC strength and fracture properties at ages ranging from 5 hours to 28 days was studied, and secondly, the effects of the environment on LMC distresses were modelled. Environmental conditions: temperature, solar energy, and wind speed were determined from weather records. A fracture mechanics based model, the Fictitious Crack Model (FCM), incorporating finite element analyses and superposition techniques was employed with material properties from the first part of study on LMC performance. Different bilinear strain softening diagrams were used to predict fracture performance at different ages. The predictions agreed well with the test data. The impacts of temperature differentials on crack development were studied. The shrinkage effect was also indirectly incorporated through the temperature analysis. The material properties study indicated significant changes in strength, deformability and fracture properties, particularly during the early age. The developments differ slightly from conventional concrete. Test results indicated a significant improvement in reducing and bridging microcracks, especially in the prepeak-load region. Fracture toughness and deformability increased significantly with time. Fracture energy varied from 2.3 to 133.1 N/m, depending on age, and to some degree, on notch depth ratio. In the second stage, the FCM provided a reasonable prediction for crack initiation and propagation when only temperature effects are of concern. Age, surface conditions and structural restraint strongly affect crack resistance of the overlays. Only slight effects were observed from the overlay thickness in the study range (51-76 mm). Shallow preexisting cracks possibly reduce the crack resistance of the overlay about 30 percent. A prolonged moist cure for 48 hours after placing is suggested to reduce the risk of cracking. With available environmental information, it is possible to develop guidelines for appropriate environmental conditions for LMC bridge deck construction to minimize the risk of early age cracking

Developmental education and teacher training

This study was designed to investigate the relationship of cognitive development and moral development; the differences and similarities between prospective elementary teachers and prospective secondary teachers in stages of cognitive development and moral development; as well as the relations between levels of cognitive and moral development and chronological age, experiences in mathematics, experiences in science, grade point average, and SAT scores. Forty-three prospective elementary teachers and 32 prospective secondary teachers were administered Piagetian cognitive and Kohlbergian moral dilemma tests in order to determine their levels of cognitive development and moral development, respectively. The Piagetian type test consisted of a proportional test and quantification of probabilities test. The data obtained were analyzed, by computer, using the t-statistic and Pearson-Product-Moment correlation coefficients

Effects of alirocumab on types of myocardial infarction: insights from the ODYSSEY OUTCOMES trial

Aims  The third Universal Definition of Myocardial Infarction (MI) Task Force classified MIs into five types: Type 1, spontaneous; Type 2, related to oxygen supply/demand imbalance; Type 3, fatal without ascertainment of cardiac biomarkers; Type 4, related to percutaneous coronary intervention; and Type 5, related to coronary artery bypass surgery. Low-density lipoprotein cholesterol (LDL-C) reduction with statins and proprotein convertase subtilisin–kexin Type 9 (PCSK9) inhibitors reduces risk of MI, but less is known about effects on types of MI. ODYSSEY OUTCOMES compared the PCSK9 inhibitor alirocumab with placebo in 18 924 patients with recent acute coronary syndrome (ACS) and elevated LDL-C (≥1.8 mmol/L) despite intensive statin therapy. In a pre-specified analysis, we assessed the effects of alirocumab on types of MI. Methods and results  Median follow-up was 2.8 years. Myocardial infarction types were prospectively adjudicated and classified. Of 1860 total MIs, 1223 (65.8%) were adjudicated as Type 1, 386 (20.8%) as Type 2, and 244 (13.1%) as Type 4. Few events were Type 3 (n = 2) or Type 5 (n = 5). Alirocumab reduced first MIs [hazard ratio (HR) 0.85, 95% confidence interval (CI) 0.77–0.95; P = 0.003], with reductions in both Type 1 (HR 0.87, 95% CI 0.77–0.99; P = 0.032) and Type 2 (0.77, 0.61–0.97; P = 0.025), but not Type 4 MI. Conclusion  After ACS, alirocumab added to intensive statin therapy favourably impacted on Type 1 and 2 MIs. The data indicate for the first time that a lipid-lowering therapy can attenuate the risk of Type 2 MI. Low-density lipoprotein cholesterol reduction below levels achievable with statins is an effective preventive strategy for both MI types.For complete list of authors see http://dx.doi.org/10.1093/eurheartj/ehz299</p

Effect of alirocumab on mortality after acute coronary syndromes. An analysis of the ODYSSEY OUTCOMES randomized clinical trial

Background: Previous trials of PCSK9 (proprotein convertase subtilisin-kexin type 9) inhibitors demonstrated reductions in major adverse cardiovascular events, but not death. We assessed the effects of alirocumab on death after index acute coronary syndrome. Methods: ODYSSEY OUTCOMES (Evaluation of Cardiovascular Outcomes After an Acute Coronary Syndrome During Treatment With Alirocumab) was a double-blind, randomized comparison of alirocumab or placebo in 18 924 patients who had an ACS 1 to 12 months previously and elevated atherogenic lipoproteins despite intensive statin therapy. Alirocumab dose was blindly titrated to target achieved low-density lipoprotein cholesterol (LDL-C) between 25 and 50 mg/dL. We examined the effects of treatment on all-cause death and its components, cardiovascular and noncardiovascular death, with log-rank testing. Joint semiparametric models tested associations between nonfatal cardiovascular events and cardiovascular or noncardiovascular death. Results: Median follow-up was 2.8 years. Death occurred in 334 (3.5%) and 392 (4.1%) patients, respectively, in the alirocumab and placebo groups (hazard ratio [HR], 0.85; 95% CI, 0.73 to 0.98; P=0.03, nominal P value). This resulted from nonsignificantly fewer cardiovascular (240 [2.5%] vs 271 [2.9%]; HR, 0.88; 95% CI, 0.74 to 1.05; P=0.15) and noncardiovascular (94 [1.0%] vs 121 [1.3%]; HR, 0.77; 95% CI, 0.59 to 1.01; P=0.06) deaths with alirocumab. In a prespecified analysis of 8242 patients eligible for ≥3 years follow-up, alirocumab reduced death (HR, 0.78; 95% CI, 0.65 to 0.94; P=0.01). Patients with nonfatal cardiovascular events were at increased risk for cardiovascular and noncardiovascular deaths (P<0.0001 for the associations). Alirocumab reduced total nonfatal cardiovascular events (P<0.001) and thereby may have attenuated the number of cardiovascular and noncardiovascular deaths. A post hoc analysis found that, compared to patients with lower LDL-C, patients with baseline LDL-C ≥100 mg/dL (2.59 mmol/L) had a greater absolute risk of death and a larger mortality benefit from alirocumab (HR, 0.71; 95% CI, 0.56 to 0.90; Pinteraction=0.007). In the alirocumab group, all-cause death declined wit h achieved LDL-C at 4 months of treatment, to a level of approximately 30 mg/dL (adjusted P=0.017 for linear trend). Conclusions: Alirocumab added to intensive statin therapy has the potential to reduce death after acute coronary syndrome, particularly if treatment is maintained for ≥3 years, if baseline LDL-C is ≥100 mg/dL, or if achieved LDL-C is low. Clinical Trial Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT01663402

EFFECT OF FLY ASH TYPE ON ASR EXPANSION OF POTENTIAL REACTIVE AGGREGATES

The Thirteenth East Asia-Pacific Conference on Structural Engineering and Construction (EASEC-13), September 11-13, 2013, Sapporo, Japan

Fabrication of highly porous mortar to alleviate failure caused by alkali-silica reaction (ASR)

Alkali-silica reaction (ASR) is one of the crucial mechanism contributing to internal failure of concrete. ASR generally involves formation of swollen alkali silicate hydrate gel, also known as ASR gel, which exerts an expansive pressure, resulting in crack in concrete. This research, hence, aims at inventing porous mortar capable of preventing cracks originated from ASR. In this study, porous mortar bars were successfully fabricated. Aluminium powder, acting as an air entrainment agent, with the concentrations ranging from 0.05 to 0.15 wt% was added to mixture of sand and cement prior to casting. Physical and microstructural examination of the mortar bars revealed that greater quantity of aluminium addition resulted in a higher porosity. Formation of the pores accommodated spaces for ASR gel and reduced the expansive pressure, which potentially led to alleviation of cracks

Synergistic effect of metakaolin and fly ash on properties of concrete

© 2017 Elsevier Ltd This paper reports the effects of the interaction between metakaolin and fly ash on the microstructure and property development of concrete. X-ray diffraction analysis revealed unstable hemicarboaluminate and calcium monocarboaluminate compounds in most mixtures during 7–28 day curing periods, the relative amounts depending on the metakaolin to fly ash ratio. The mix with the highest peaks of the monocarboaluminate phase yielded the highest long-term strength. Significant improvements in terms of durability, abrasion resistance, chloride permeability and steel corrosion risk were observed. A proportion of cement:metakaolin:fly ash as 80:10:10 yielded marked improvements on slump, slump loss and long- term strength. Synergistic action in the ternary blend significantly improved the workability of fresh concrete and yielded a more uniform mix, denser microstructure and better performance of the hardened concrete