凍融損傷噴射混凝土本構關系及微觀結構

王家濱　牛荻濤　袁斌

摘要：采用棱柱體試件，通過快速凍融試驗方法，對凍融損傷后同配合比普通混凝土、噴射混凝土及鋼纖維噴射混凝土單軸受壓應力應變全曲線進行研究。對應力應變關系中相關參數進行回歸分析，得出凍融循環后試件應力應變全曲線方程。結果表明：隨著凍融循環次數增加，受壓應力應變曲線趨于扁平；峰值應力降低，峰值應變增大，分別與凍融循環次數呈線性和指數變化。與普通混凝土相比，噴射混凝土峰值應力下降速率小，而鋼纖維噴射混凝土的下降速率進一步減小。而后，采用掃描電子顯微鏡及壓汞法，對損傷后試件微觀結構和孔結構進行觀察分析，發現隨著凍融循環次數增加，在滲透壓和凍脹壓力綜合作用下，試件內部微裂紋及氣孔增多，孔徑增大，試件密實度顯著降低；而鋼纖維噴射混凝土中僅出現少量連通毛細孔，這與宏觀力學性能變化呈現一致性。

關鍵詞：隧道工程；噴射混凝土；凍融損傷；應力應變曲線；微觀結構

中圖分類號：TU502.6；TU528.53

文獻標志碼：A文章編號：16744764（2016）01003010

Abstract：

Using prismatic specimens of concrete， we examined the uniaxial compression stressstrain curve of ordinary concrete （mixture C43F10）， ordinary shotcrete （mixture S43F10） and steel fiber reinforced shotcrete （mixture S43F10SF50） with the same mixture by using the accelerating freezethaw method. By fitting the relationship between parameters and the number of freezethaw cycles， the stressstrain curve of specimens under damaging was calculated. The test results show that with the increase of freezing and thawing cycles， the peak stress is low and has a liner relation with the freezing and thawing cycles. However， the peak strain is bigger and demonstrates an exponential relationship. The peak stress of shotcrete decreases more slowly than that of ordinary concrete， and that of shotcrete with steel fiber reduces much more slowly.

We also observed and analyzed the microstructure and pores of specimens after damage by using scanning electron microscope and the mercury intrusion method. The result shows that with an increase number of freezethaw cycles，

the amount of microcreaks and pores

and the diameter of pores increase by the effect of osmotic pressure and frost heave pressure while the specimens density decreases. In the same situation， there are only several connected capillary pores in steel fiber reinforced shotcrete， which is consistent with macromechanical properties.

Keywords：tunnel engineering； shotcrete； freeze and thaw damage； stressstrain curve； microstructure

噴射混凝土是在高壓空氣作用下，通過管道將混凝土均勻噴射在受噴面上的一種特殊混凝土[13]。因速凝劑的摻入，噴射混凝土具有極短的終凝時間、高早齡期強度，其1 h抗壓強度可達2 MPa，故廣泛應用在隧道襯砌結構、礦山巷道支護、邊坡工程及橋梁結構維修加固等場所[47]。隨著現代隧道施工技術進步，噴射混凝土及鋼纖維噴射混凝土單層永久襯砌成為隧道襯砌結構發展趨勢[8]。……