Experimental Study On The Filling Capacity Of SCC And The Microscopic Properties Of The Interfaces In RFC

Rock-filled concrete (RFC) is a novel large-scale concrete constructiontechnology based on self-compacting concrete (SCC). It has many advantages suchas faster construction speed, less CO2emission, etc. RFC technology has beenapplied in over40projects in China. Nonetheless, these advantages come withconcerns, among which two of the most controversial issues in RFC research andapplication are (1) whether SCC can effectively fill the spaces between large rocksand (2) whether the distinctive casting process and the application of large rockswill affect the properties of the rock/SCC interfaces. Currently researches aboutthese two issues are limited to engineering experience and some large-scale testresults, calling for further study about the basic physical mechanism behind theseissues. By conducting a series of experiments, this thesis aims to explore thefundamental mechanism of these two issues and analyze the influence of relatedparameters, which may provide theoretical and experimental basis for designing,choosing suitable parameters and quality evaluation of RFC construction projects.Multi-scale method was used to study the filling capacity of SCC. By means ofself-designed experiment, the flow process of both self-compacting grout (SCG) andself-compacting mortar (SCM) was simulated. Based on fluid blocking model andgranular blocking model, the filling capacity and blocking mechanism of both SCG andSCM were investigated and discussed, and the application scope of these two modelswas discussed. Furthermore, by comparing results of different experiments, the effectsof several parameters were also investigated. On the basis of the granular blockingmodal proposed by Roussel, the passing ability of SCC was investigated using animproved experimental setup. The passing ability and blocking mechanism of SCCwere analyzed and discussed, making Roussel’s model more applicable to RFCconstruction. A novel method for testing the filling capacity of SCC in rock skeletonusing porous medium (PM) filling method was proposed, the relation between yieldstress of SCC (SCM) and filling performance was found by theoretical anaylais andvalidated by PM filling test. At last, the cavity-filling ability of SCC that is concernedby many engineers was also investigated by self-designed experiment. On the other hand, to study the properties of the interfaces in RFC, severalresearch methods of investigating the microscopic properties of cementitiousmaterial were reviewed and compared, and two of them (BSE and nanoindentation)were selected as effective methods. After that, both BSE and nanoindentation testwere conducted at identical positions of a number of samples from model RFCspecimen. By comparing the results of these two tests, the relation betweenporosity and elastic modulus at micro scale was obtained. Based on this relation,both aggregate/grout interface and aggregate/mortar interface of model RFCspecimen casted by SCG and SCM were investigated using BSE test and imageanalysis. The porosity and elastic modulus of these interfaces were calculated.Relied on these results, the effects of different parameters on the microscopicproperties of the interfaces in model RFC specimen were analyzed. By comparingwith conclusions of existing study on conventional concrete, the distinctivecharacteristics of the interfaces in RFC were proposed.