D0I:10.13374/i.issn1001-053x.1989.06.032 第11卷第6期 北京料技大学学报 Vol.11 No.6 1989年11月 Journal of University of Science and Technology Beijing Nov.1989 Microcracks in MDF Cement' Shang Chengjia(尚成嘉)，Zhi Rentao(职任涛)，Zhu Fengwu(朱逢吾)， Zhou Zhengqian(周政谦)，Xiao Jimei(肖纪美)* 八 ABSTRACT:The relationspip between the microcracks and the mechanical behaviors and the characteristics of fracture of MDF cement have been studied. The results show that most of the microcracks lie and propagate in the matrix or along the boundary of the clinkers.The microcracks improve the toughness of MDF cement.The Griffith's equation is invalid to describe the fracture of MDF cement. KEY WORDS:cement,microcrack,MDF MDF cement was firstly reported in 1981 by Birchall et al.1.Since than, interests have been raised to discover the strengthening mechanism of MDF cement. Some authors t2s,1 considered that the high strength of 70-150 MPa is due to the reduction of the pore size,which is about 1.0mm in hardened cement paste (HCP)and less than 20gm in MDF cement.They proposed to apply Griffith's equation to explain the relationship between flexural strength and pore size.But when the pore size is less than 100um,the flexural strength dose not further increase with the decrease of pore size.They guessed that the flaws other than pores were becoming important.e.g.the large angle cement grain- boundaries and cement-polymer interfaces would play the dominent part in deter- mining strength. However,Eden and Baileyts showed the flexural strength can only be increased to as high as 20MPa when the pore size was reduced to less then 100um by mixing under vacuum with a small addition of a plasticizer.So they suggested that the principle role of the polymer was to act as an adhesive which assisted the strength developed by the hydrated cement.Moreover,Sindair and Grovest61 and Rodger et al.t71 have showed there are chemical reactions between polymer and cement.In a word,the strengthening mechanism of MDF cement is complex Manuscript Received July 17,1989 ··Dept,of Material Physics 585第 卷第 期 年 月 北 京 科 技 大 学 学 报 一 已 。 ’ 尚 成 嘉 ， 职 任 涛 ， 脚 朱 逢吾 夕 周政 谦 ， ， 肖纪 美广 尹、 。 ， ， ， 叹 、 ， · ’ ， 一 卜 ， 。 拼 · ’ · 拼 ， · · · 一 ， 拼 · 皿 · ， 。 · ， ， ， 二 DOI ：10．13374／j ．issn1001－053x．1989．06．032