Strength Of Controlled Low-strength Material Research Articles

Geopolymeric flocculation-solidification of tail slurry of shield tunnelling spoil after sand separation

Geopolymeric flocculation-solidification of the tail slurry of shield tunnelling spoil after sand separation was investigated to replace the low-efficient flocculation and filter-pressing method currently adopted on site. The geopolymeric flocculation-solidification agent (GBFS-FS) consisting of flocculation component and geopolymeric solidification component (granulated blast-furnace slag (GBFS) activated by alkali) was prepared and investigated through flocculation-sedimentation test, dewatering model test, unconfined compression test, SEM test, etc. In the flocculation-sedimentation test, the GBFS-FS agent demonstrated the best flocculation effect as compared with other cementitious flocculation-solidification agents. The dewatering model tests revealed that adding the GBFS-FS agent into the slurry can not only dewater the slurry efficiently, but also generate solidified clayey sediments with quickly-increased strength. The solidified clayey sediments with GBFS-FS showed strengths 3.5 times higher than others with cementitious agents at a 28-day curing age. The GBFS-FS agent can also facilitate to make controlled low-strength material (CLSM) using the tail slurry. The fluidity and strength of CLSM with GBFS-FS were distinctly better than those of other groups. SEM test shows that the components of the GBFS-FS agent can interact to avoid large flocs and support each other in strength growth.

Experimental Investigation of Utilizing Industrial Waste and Byproduct Materials in Controlled Low Strength Materials (CLSM)

Laboratory experiments were conducted in this study to investigate the suitability and applicability of incorporating fly ash, bottom ash and paper sludge with various contents into CLSM mixtures. Fly ash was used as a substitute for Portland cement, bottom ash was added by partially replacing fine aggregate, while paper sludge was treated as a fibrous admixture. Physical and mechanically properties of the CLSM mixtures were examined through flowability, compressive strength, and splitting tensile strength tests. The test results indicated that both fly ash and bottom ash can be potentially used as basic materials for CLSM mixtures with desirable performances, and by limiting the amount of cement used in the mixture, the ultimate strength of CLSM could be easily controlled available for excavation. The strength of the CLSM mixtures were reduced to some extent by incorporating high content of fly ash, while they were significantly increased with high content of natural sand replaced by bottom ash. Due to the high water absorption of the paper sludge, the mixture with paper sludge added exhibited relatively low flowability, and it showed no benefits on enhancing compressive and splitting tensile strengths as common fibrous materials.

Use of Recycled Concrete Aggregate in Controlled Low-Strength Material (CLSM)

Use of recycled concrete aggregate (RCA) is getting importance as it minimizes the use of fresh materials and eliminates waste disposal. One of the uses of RCA is as aggregate in Controlled Low Strength Material (CLSM). This paper reports the results of the investigation done on the use of RCA in CLSM. Various mixtures of CLSM were made using RCA, fly ash, and cement. Tests for workability, bleeding, density, strength, water absorption, sorption, and ultrasonic pulse velocity (UPV) were conducted. Results show that the compressive strength ranged from 1.71 MPa to 4.92 MPa, fresh density from 1879 kg/m3 to 1998 kg/m3. The strength of CLSM increases with the increase in fly ash; water absorption and bleeding decrease with increase in fly ash. It is concluded that the RCA has potential to be used in CLSM and the addition of fly ash enhances the performance.

Load Transfer Analyses of Buried Pipe in Different Backfills

Nonlinear finite-element analyses have been carried out to assess the effects of different trench backfill materials, pipe burial depths, and pipe materials on the amount of traffic load transferred to buried pipe. The analyses show that the use of trench backfills such as controlled low strength material (CLSM) instead of traditional materials such as sand and clay, results in significantly reduced stresses in polyvinyl chloride (PVC) pipe under traffic loading. This finding is in agreement with recent truck load tests carried out in the City of Edmonton, where strains were monitored on buried PVC water mains. The protection of buried pipes under or in CLSM backfill from traffic loading becomes more significant with the decrease in pipe burial depth and stiffness. The reasons behind the difference in load transfer between the traditional backfills and CLSM are the high elastic modulus and strength of CLSM, as well as uniform load transfer along the longitudinal axis of the pipe.