Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. I...Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. In this work, the possibility of using micro-size metakaolin(MSK) particles to improve the compressive strength of HVFA paste before and after subjecting to high temperatures was studied. To produce HVFA paste, cement was partially substituted with 70% fly ash(FA), by weight. After that, FA was partially substituted with MSK at ratios fluctuating from 5% to 20% with an interval of 5%, by weight. The effect of MSK on the workability of HVFA mixture was measured. After curing, specimens were subjected to different high temperatures fluctuating from 400 to 1000 ℃ with an interval of 200 ℃ for 2 h. The results were analyzed by different techniques named X-ray diffraction(XRD), thermogravimetry(TGA) and scanning electron microscopy(SEM). The results showed that the incorporation of MSK particles into HVFA mixture exhibited a negative effect on the workability and a positive effect on the compressive strength before and after firing.展开更多
BACKGROUND：High-volume hemofiltration （HVHF） is technically possible in severe acute pancreatitis （SAP） patients complicated with multiple organ dysfunction syndrome （MODS）. Continuous HVHF is expected to becom...BACKGROUND：High-volume hemofiltration （HVHF） is technically possible in severe acute pancreatitis （SAP） patients complicated with multiple organ dysfunction syndrome （MODS）. Continuous HVHF is expected to become a beneficial adjunct therapy for SAP complicated with MODS. In this study, we aimed to explore the effects of fluid resuscitation and HVHF on alveolar- arterial oxygen exchange, the Acute Physiology and Chronic Health Evaluation II （APACHE II） score in patients with refractory septic shock. METHODS：A total of 89 refractory septic shock patients, who were admitted to ICU, the Provincial Hospital affiliated to Shandong University from August 2006 to December 2009, were enrolled in this retrospective study. The patients were randomly divided into two groups： fluid resuscitation （group A, n=41）, and fluid resuscitation plus high-volume hemofiltration （group B, n=48）, The levels of O2 content of central venous blood （CcvO2）, arterial oxygen content （CaO2）, alveolar-arterial oxygen pressure difference P（A-a）DO2, ratio of arterial oxygen pressure/alveolar oxygen pressure （PaO2/ PAO2）, respiratory index （RI） and oxygenation index （OI） were determined. The oxygen exchange levels of the two groups were examined based on the arterial blood gas analysis at different times （0, 24, 72 hours and 7 days of treatment） in the two groups. The APACHE II score was calculated before and after 7-day treatment in the two groups. The levels of CcvO2, CaO2 on day 7 in group A were significantly lower than those in group B （CcvO2：0.60±0.24 vs, 0.72±0.28, P〈0.05; CaO2：0.84±0.43 vs. 0.94±0.46, P〈0.05）. The level of oxygen extraction rate （O2ER） in group A on the 7th day was significantly higher than that in group B （ 28.7±2.4 vs. 21.7±3.4, P〈0.01）. The levels of P（A-a）DO2 and RI in group B on the 7th day were significantly lower than those in group A. The levels of PaO2/PAO2 and OI in group B on 7th day were significantly higher than those in group A （P〈0.05 or P〈0.01）. The APACHE II score in the two groups reduced gradually after 7-day treatment, and the APACHE II score on the 7th day in group B was significantly lower than that in group A （8.2±3.8 vs. 17.2±6.8, P〈0.01）. HVHF combined with fluid resuscitation can improve alveolar- arterial-oxygen exchange, decrease the APACHE II score in patients with refractory septic shock, and thus it increases the survival rate of patients.展开更多
The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonat...The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.展开更多
HVFA （high-volume fly ash） concrete could be a sustainable way for by-product utilization to conserve natural resources and protect environment. HVFA concrete can play the role of a high-performance material that ma...HVFA （high-volume fly ash） concrete could be a sustainable way for by-product utilization to conserve natural resources and protect environment. HVFA concrete can play the role of a high-performance material that may be comparable to the conventional Portland cement concrete. The results of the research programme concerning the relationships between the composition of concrete （w/b ratio, fly ash content and type of cement） and their physical and mechanical properties are presented and discussed in the paper. It is found that the introduction of high-volume fly ash into concrete has caused a decrease in compressive strength at the early age of storage. The significant increase in strength was observed between 28 days and 90 days of curing. The high-volume fly ash concretes were characterized with lower water absorbability and sorptivity than control concrete.展开更多
文摘Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. In this work, the possibility of using micro-size metakaolin(MSK) particles to improve the compressive strength of HVFA paste before and after subjecting to high temperatures was studied. To produce HVFA paste, cement was partially substituted with 70% fly ash(FA), by weight. After that, FA was partially substituted with MSK at ratios fluctuating from 5% to 20% with an interval of 5%, by weight. The effect of MSK on the workability of HVFA mixture was measured. After curing, specimens were subjected to different high temperatures fluctuating from 400 to 1000 ℃ with an interval of 200 ℃ for 2 h. The results were analyzed by different techniques named X-ray diffraction(XRD), thermogravimetry(TGA) and scanning electron microscopy(SEM). The results showed that the incorporation of MSK particles into HVFA mixture exhibited a negative effect on the workability and a positive effect on the compressive strength before and after firing.
基金This study was supported by a grant from the Natural Science Foundation of Shandong Province （Y2006C77）.
文摘BACKGROUND：High-volume hemofiltration （HVHF） is technically possible in severe acute pancreatitis （SAP） patients complicated with multiple organ dysfunction syndrome （MODS）. Continuous HVHF is expected to become a beneficial adjunct therapy for SAP complicated with MODS. In this study, we aimed to explore the effects of fluid resuscitation and HVHF on alveolar- arterial oxygen exchange, the Acute Physiology and Chronic Health Evaluation II （APACHE II） score in patients with refractory septic shock. METHODS：A total of 89 refractory septic shock patients, who were admitted to ICU, the Provincial Hospital affiliated to Shandong University from August 2006 to December 2009, were enrolled in this retrospective study. The patients were randomly divided into two groups： fluid resuscitation （group A, n=41）, and fluid resuscitation plus high-volume hemofiltration （group B, n=48）, The levels of O2 content of central venous blood （CcvO2）, arterial oxygen content （CaO2）, alveolar-arterial oxygen pressure difference P（A-a）DO2, ratio of arterial oxygen pressure/alveolar oxygen pressure （PaO2/ PAO2）, respiratory index （RI） and oxygenation index （OI） were determined. The oxygen exchange levels of the two groups were examined based on the arterial blood gas analysis at different times （0, 24, 72 hours and 7 days of treatment） in the two groups. The APACHE II score was calculated before and after 7-day treatment in the two groups. The levels of CcvO2, CaO2 on day 7 in group A were significantly lower than those in group B （CcvO2：0.60±0.24 vs, 0.72±0.28, P〈0.05; CaO2：0.84±0.43 vs. 0.94±0.46, P〈0.05）. The level of oxygen extraction rate （O2ER） in group A on the 7th day was significantly higher than that in group B （ 28.7±2.4 vs. 21.7±3.4, P〈0.01）. The levels of P（A-a）DO2 and RI in group B on the 7th day were significantly lower than those in group A. The levels of PaO2/PAO2 and OI in group B on 7th day were significantly higher than those in group A （P〈0.05 or P〈0.01）. The APACHE II score in the two groups reduced gradually after 7-day treatment, and the APACHE II score on the 7th day in group B was significantly lower than that in group A （8.2±3.8 vs. 17.2±6.8, P〈0.01）. HVHF combined with fluid resuscitation can improve alveolar- arterial-oxygen exchange, decrease the APACHE II score in patients with refractory septic shock, and thus it increases the survival rate of patients.
文摘The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.
文摘HVFA （high-volume fly ash） concrete could be a sustainable way for by-product utilization to conserve natural resources and protect environment. HVFA concrete can play the role of a high-performance material that may be comparable to the conventional Portland cement concrete. The results of the research programme concerning the relationships between the composition of concrete （w/b ratio, fly ash content and type of cement） and their physical and mechanical properties are presented and discussed in the paper. It is found that the introduction of high-volume fly ash into concrete has caused a decrease in compressive strength at the early age of storage. The significant increase in strength was observed between 28 days and 90 days of curing. The high-volume fly ash concretes were characterized with lower water absorbability and sorptivity than control concrete.
