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The effects of drying techniques on the compr-essive strength of gypsum products

Authors: Radhwan H Hasan --- Kasim A Mohammad
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2005 Volume: 5 Issue: 1 Pages: 63-68
Publisher: Mosul University جامعة الموصل

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Abstract

Excess water in set dental stone decreases its strength.So different methods were used to expel excess water but thecompressive strength may be affected by drying technique.The purpose of this study was to evaluate the compressive strengthof two types of set dental stone after air, conventionaloven and microwave drying techniques.A total of 60 stone specimens (30 specimens made fromSilky Rock stone and 30 Zeta stone) were prepared by the aidof an acrylic split mold according to ADA Specification No.25. Specimens were divided into six groups of 10 identicalspecimens for each. Then groups were either dried by air,conventional oven or microwave oven. Using UnconfinedCompression Machine, the specimens were loaded by a crosshead speed of 1 mm/minute till the specimen being fractured.The load required to fracture the stone specimens was recordedand analyzed using analysis of variance followed by Duncan’sMultiple Range Test for the statistical comparisons betweendrying techniques at a significance level of p< 0.05, andStudent’s t–test was used to compare between the two stonetypes.The results revealed that high significant differenceswere present between the different drying techniques(p<0.0001) with air dried specimens were significantly strongerthan others and microwave dried specimens were significantlystronger than conventional oven dried specimens. SilkyRock (type IV) stone was significantly stronger than Zeta(type III) stone (p<0.001).From this study, it could be concluded that the highestcompressive strength can be obtained by air drying of the stonefor 24 hours, while microwave drying technique give betterresults than conventional oven drying technique with theadvantage of time saving over the two other drying techniques.


Article
INFLUNCE OF INCREASING WATER:CEMENT RATIO ON THE SOME PROPERTIES OF CONCRETE CONTAINS LOW CONTENT OF POLYMER

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Abstract

الخلاصة:تضمن هذا البحث دراسة تأثير تغير نسبة الماء/الاسمنت على بعض خواص الخرسانة المحتوية على نسبة واطئه من بوليمر مطاط الستايرين بيوتادين SBR كمقاومة الانضغاط , مقاومة الانثناء , الكثافة وقابلية التثغيل. استخدمت نسبة الخلط الوزنية ( 4:2:1) واضيف البوليمر كنسبة وزنية من الاسمنت وهي 2%. استعملت خلطة مرجعية لغرض المقارنة. كانت نسب الماء /الاسمنت 0.2, 0.3 , 0.4, 0.5 و 0.6 بينما استخدمت نسبة 0.35 للخرسانة المرجعية. تراوحت قيم الكثافة ما بين 2030 و 2360 كغم/م3 . أدت زيادة نسبة الماء/السمنت الى زيادة الهطول. كان لنسبة البوليمر:السمنت الواطئة تأثيراً واضحاَ في تحسين مقاومة الانثناء فيما كان تأثيرها أقل وضوحاً في تحسين مقاومة الانضغاط للخرسانة موضوع البحث.

1-AbstractThis research includes the variation effect of (W/C) water: cement ratio on the properties as compressive strength , flxural strength , density and workability of concrete contains low Polymer SBR ratio.1:2:4 (cement: sand :gravel) by weight mixes were used . The polymer was added as percentages of cement weight and it was 2%. Reference mix was made. Water cement ratio (w/c) were used are 0.2 , 0.3 , 0.4 , 0.5 and 0.6 respectively and 0.35 (w/c) was used for reference mix . The density of concrete varied between 2030 kg/m3 and 2360 kg/m3.

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