Development and Application of a High-Volume Recycled Powder Solidifying Material for Waterworks Sludge

Recycled powder(RP)is produced as a by-product during the process of recycling construction and demolition(C&D)wastes,presenting a low additional value.Using RP-based solidifying material can not only improve its utilization efficiency,but also reduce the cost of commercial solidifying materials.To date,this is the best solidifying material utilized to dispose the original waterworks sludge(OWS)with high moisture contents(60%),and the product could be used to fabricate non-fired bricks.This has become a new environment-friendly technology of“using waste to treat waste”.In this paper,the influence of different particle sizes and dosages of RP on the prepared solidifying material was studied.Besides,unconfined compression strength(UCS),volume stability,chemical composition,and heat of hydration,pore structure of the solidifying material were characterized.Then,non-fired bricks were prepared by using the solidifying material,recycled aggregate,and original waterworks sludge.The UCS and softing coefficient(SC)of the non-fired bricks were evaluated.As a result,the 28-day UCS of the solidifying material with optimal(M30)was 35.40 MPa,which could reach 84.37%of Portland cement(PC).The addition of RP increased the volume stability of the solidifying material.The addition of a large amount of RP reduced the heat flux and cumulative heat release of the solidifying material,while its porosity increased.The UCS of non-fired brick(NF20)in 28 days was 15.19 MPa and the SC after 28 days was 78.35%.In conclusion,the preparation of solidifying material using RP could be a promising approach and has a great potential in disposal of original waterworks sludge.

Coal and gas outburst prevention using new high water content cement slurry for injection into the coal seam

As coal and gas outburst is one of the most serious mine disasters, it is very important to at least control it if not prevent it from occurring. Injecting cement slurry or grouting into the coal seam can strengthen the seam, increase its rigidity coefficient(f), and reduce the volumetric expansion due to gas energy release.This paper reports the results of laboratory experiments on cement-based high water content slurry having different water-cement ratios(W/C) to be used for coal injection. The results show that as the W/C increases, the mobility of the slurry and its setting time increase. The compressive strength and rupture strength, however, are reduced. Furthermore, high W/C grout shows early strength after 7 days, which can be 80% of its 14-day compressive strength. To achieve rapid setting and early strength, the addition of Na_2SiO_3has proven to give the best result, when the concentration of the additive is 3%. The initial and final setting times are 13 and 21 min shorter than samples without Na_2SiO_3, while the compressive strength is more than double. As a retarder, the initial setting time can be extended to 83 min when tartaric acid of 0.4% concentration is added. Through the orthogonal experiment, the optimum recipe of the new high water content slurry has been determined to be: W/C = 2, tartaric acid = 0.2%, Na_2SiO_3= 3%, and12% bentonite. Reinforcement by injection simulation experiments show that the grouting radius of the new slurry mix is 250 mm when the applied grouting pressure is 60 k Pa, 7-day rupture strength and compressive strength are 5.2 and 6.4 MPa, respectively, and are 37% and 88% higher than ordinary cement grout. It can be concluded that the newly developed slurry mix is more effective than the ordinary mix for reinforcing coal and controlling gas outburst.

Development and Field Application of Phosphogypsum-Based Soil Subgrade Stabilizers

A phosphogypsum-based subgrade stabilizer(PBSS)was formulated using industrial by-product phosphogypsum(PG),mixed with slag and calcium-silicon-rich active material(GSR).The active powder(AP)was used to modify PBSS,and PBSS-AP was obtained.PBSS and PBSS-AP were each mixed with 10%silty soil,and cement and lime(CAL:5%lime+2%cement)were used as the traditional material for comparative experiments.Samples were cured under standard conditions,and tested for unconfined compressive strength(UCS),water stability,volume expansion,and leachate,to explore the stabilization effect of the three solidified materials on silty soil.The results showed that the comprehensive performance of sility soil mixed with 12%PBSS-AP was the best.The CaO,SiO_(2)and Al_(2)O_(3)provided by PG,Slag and GSR will react with water to form a stable C-S-H gel,which is conducive to stabilizing the soil.Field application results showed that the compaction exceeded 95%,the deflection was 144.9 mm,and UCS was 2.5 MPa after 28 days.These findings indicated that PBSS-AP is an effective stabilizer for subgrade soils.

Situation and Prevention of Loess Water Erosion Problem along the West-to-East Gas Pipeline in China

Loess water erosion constitutes a great threat to the safety of the West-to-East Gas Pipeline in China. Through aerial-photo interpretation and investigation of the typical region （Zichang （子长）-Yongping （水坪） Section） where the loess water erosion problem is intensely developed, the influence of water erosion on the pipeline in the loess area can be manifested as the following 3 aspects： （1） surface and gully erosion causes the base overhead and pipeline exposure; （2） underground erosion forms caves, which may cause surface subsidence and foundation failure; （3） water erosion of loess may destroy the balance of slopes and cause geological hazards like landslide, collapse and debris flow. Presently, the controlling methods are mainly concrete or grouted rubble protection. These methods are not only high in cost but also have poor effect and poor durability. This article suggests a method of controlling the loess water erosion problem with soil solidified material. Then, related tests are conducted. The results of uniaxial compression, permeability, and anti-erosion ability tests indicate that the mechanical properties and anti-erosion ability of solidified loess were improved significantly.