Effect of chemical admixture on property of fresh mortar using sludge water

Addition of sludge water as a part of mixing water had little influence on strength and durability of hardened concrete, but caused a slump decrease of fresh concrete. The decrease of slump was improved by addition of a certain set retarder such as gluconate into sludge water due to control of cement hydration. Some of polymers were also effective in improvement of slump. However hydration of cement was observed in those cases of polymers. Therefore it is presumed such the polymers improve slump not by hydration control effect but by another one

Influence of Coarse Aggregate on the Shrinkage of Normal and High-Strength Concretes

Inclusion of aggregates leads to a reduction in drying shrinkage of cement paste. This is due to the elastic deformation of the aggregates that partly restrains the shrinkage deformation of cement paste. Hence, concrete with higher aggregate content exhibits smaller shrinkage. In addition, concrete with aggregates of higher modulus of elasticity or of rougher surfaces is more resistant to shrinkage process. In this paper the effects of the type of coarse aggregate on the shrinkage of normal and high-strength concretes are investigated. Two different types of crushed stone were used as coarse aggregates to produce the concrete mixtures used in this study. For each coarse aggregate type, two normal-strength concrete (NSC) mixtures and two high-strength concrete (HSC) mixtures were prepared. The 28-day compressive strength values of NSC mixtures were about 35 and 50 MPa, while those of HSC mixtures were 70 and 100 MPa, respectively. All shrinkage specimens were cured in water for 14 days after casting, then exposed to drying under the conditions of constant temperature (20℃) and relative humidity (60%). It has been shown that the type of the coarse aggregate influences shrinkage behaviour of both normal and high-strength concretes

THE SULFURIC ACID RESISTANCE OF CONCRETE WITH BLAST FURNACE SLAG

The deterioration of concrete by sulfuric acid attack in sewage environments has become a serious problem. In this study, it was shown that the resistance to sulfuric acid of mortar and concrete can be improved by using a blast-furnace slag fine aggregate to the total amount of fine aggregate. When mortar or concrete reacts to sulfuric acid, dihydrated gypsum film is formed around the particulate of the fine aggregate. This dihydrated gypsum film could retard the penetration of sulfuric acid, thus improving the resistance to sulfuric acid. However, the resistance to sulfuric acid depends on the hardness of the dihydrated gypsum film

Strength and Durability of Concrete with Blast Furnace Slag

The properties of concrete using blast furnace as binder and fine aggregate have been investigated in this study. The experiments focus on the properties of concrete such as compressive strength and young's modulus, carbonation, diffusion of chloride ions, resistance to sulfate attack and resistance to freeze and thaw. The experimental results show that when blast furnace slag is used in concrete, it improves the durability properties of concrete. However, the combination of using both blast furnace slag as binder and fine aggregate shows a greater improvement of those properties of concrete

Impact of Portlandite on Alkali-Silica Reaction of Pyrex Glass and Blastfurnace Slag Aggregate

In this study, it is investigated the effect of Ca ion on dissolution and reaction products in alkaline environment using Pyrex glass showing ASR expansion and blast furnace slag fine aggregate suppressing ASR. It is reported that Ca plays a role in the dissolution and polymerization of silica, and is therefore an important factor in ASR. For each sample, calculation of dissolution rate and analysis of solid phase product by 29Si MAS NMR and XRD/Rietveld analysis, and liquid phase analysis by ICP-AES were performed. As a result, it was confirmed that addition of Ca has an influence on dissolution behavior of PG and BFS. In the reaction of PG, addition of Ca promotes the polymerization reaction of silica and increases the amount of N-S-H which has expandable and contributes to deterioration mechanism. On the other hand, in BFS, the dissolved silica did not polymerize and N-S-H did not form. It was suggested that the difference in ASR reactivity between PG and BFS is due to the difference in the reaction behavior

Effect of Blast Furnace Slag Sand to Durability of Concrete

本研究は，高炉スラグを用いたコンクリートの中性化，耐硫酸塩性および凍結融解 抵抗性の検討を行ったものである．高炉スラグを細骨材に用いることで，細骨材周辺に集 積する水酸化カルシウムがなくなり，骨材表面とペーストとの界面が強固なものとなるた め，コンクリートの中性化および耐硫酸塩性が向上する．また，結合材の一部を高炉スラ グ微粉末に置き換えるか，または，細骨材に高炉スラグ細骨材を用いたコンクリートでは， AE 剤を用いることなく，また，蒸気養生を行っても，十分な凍結融解抵抗性が得られる

Relationship between oral hygiene knowledge, source of oral hygiene knowledge and oral hygiene behavior in Japanese university students: A prospective cohort study

The aim of this prospective cohort study was to examine whether oral hygiene knowledge, and the source of that knowledge, affect oral hygiene behavior in university students in Japan. An oral exam and questionnaire survey developed to evaluate oral hygiene knowledge, the source of that knowledge, and oral hygiene behavior, such as the frequency of tooth brushing and regular dental checkups and the use of dental floss, was conducted on university student volunteers. In total, 310 students with poor tooth brushing behavior (frequency of tooth brushing per day [ 50%) source of oral hygiene knowledge, and that a more frequent use of dental floss was significantly associated with dental clinics being a source of oral hygiene knowledge (OR, 4.11; 95%CI, 1.871-9.029; p < 0.001). In addition, a significant association was seen between dental clinics being a source of oral hygiene knowledge and more frequent regular dental checkups (OR, 13.626; 95%CI, 5.971-31.095; p < 0.001). These findings suggest the existence of a relationship between dental clinics being the most common source of oral hygiene knowledge and improved oral hygiene behavior in Japanese university students

Association between Household Exposure to Secondhand Smoke and Dental Caries among Japanese Young Adults: A Cross-Sectional Study

The long-term effects of secondhand smoke (SHS) on dental caries among Japanese young adults remain unclear. The purpose of this cross-sectional study was to evaluate whether household exposure to SHS is associated with dental caries in permanent dentition among Japanese young adults. The study sample included 1905 first-year university students (age range: 18-19 years) who answered a questionnaire and participated in oral examinations. The degree of household exposure to SHS was categorized into four levels according to the SHS duration: no experience (-), past, current SHS = 10 years. Dental caries are expressed as the total number of decayed, missing, and filled teeth (DMFT) score. The relationships between SHS and dental caries were determined by logistic regression analysis. DMFT scores (median (25th percentile, 75th percentile)) were significantly higher in the current SHS >= 10 years (median: 1.0 (0.0, 3.0)) than in the SHS-(median: 0.0 (0.0, 2.0)); p = 0.001). DMFT >= 1 was significantly associated with SHS >= 10 years (adjusted odds ratio: 1.50, 95% confidence interval: 1.20-1.87, p = 10 years) was associated with dental caries in permanent dentition among Japanese young adults