Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

The fractured surrounding rocks of roadways pose major challenges to safe mining.Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks.The aim of this study is to develop highly efficient composite ultrafine cement(CUC)grouts to reinforce the roadway in fractured surrounding rocks.The materials used are ultrafine cement(UC),ultrafine fly ash(UF),ultrafine slag(US),and additives(superplasticizer[SUP],aluminate ultrafine expansion agent[AUA],gypsum,and retarder).The fluidity,bleeding,shrinkage,setting time,chemical composition,microstructure,degree of hydration,and mechanical property of grouting materials were evaluated in this study.Also,a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock.The results have shown that the addition of UF and US reduces the plastic viscosity of CUC,and the best fluidity can be obtained by adding 40%UF and 10%US.Since UC and UF particles are small,the pozzolanic effect of UF promotes the hydration reaction,which is conductive to the stability of CUC grouts.In addition,fine particles of UC,UF,and US can effectively fill the pores,while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout.The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts.Finally,the CUC22‐8 grout was used to reinforce the No.20322 belt roadway.The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway.In this research,high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

The Rheological Properties of Ultra-fine High Performance Grouting Cement

The material properties of surface and powder, rheological property, and mineral composition were investigated by means of SEM, XRD, Malvern laser granulometer and rotary, viscometer. The influence of a admixture on ultra-fine cement rheological properties and its mechanism, were studied in material theories. The results show that the ultra-fine fly ash has a higher zeta potential, and improves flowability of ultra-fine cement paste, decreases flowability loss as time prolonging, improves compatibility between superplasticizers and cement because of the electrostatic repulsion, ball bearing effect, filling and dispersing effect of admixtures and delay-releasing effect of superplasticizers.

Preparation and Performance Research of Cement-based Grouting Materials with High Early Strength and Expansion

Main performance of the cement grouting materials made up by Portland cement（PC） and sulphoaluminate cement（SAC） was investigated in this program, a kind of expanding agent（EA） which was mainly constituted by metakaolin and alunite was utilized for the compensation of the shrinkage, the hydration products and micro structure of the grouting materials were researched by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results showed that a high expansion rate of the grouting materials could be reached as the expanding agent mixed in 6% of PC mass; the addition of SAC in the S2（PC：SAC：EA=34：6：2.25） brought a further improvement of the expansion rate of the grouting materials, the analysis of XRD and SEM showed that due to the reaction of expanding agent and SAC in the grouting materials, more ettringite crystal was generated, which resulted in a higher early strength, the addition of SAC played an expansion and strength reinforcement role in the grouting materials.

Hydraulicity of Wet-milling Ultra-fine Grouting Cement

The physical and mechanical properties of wet-milling ultra-fine grouting cement were studied,and its microstructure was observed through modern instrumentation analysis such as scanning electronic microscopy(SEM),X-ray diffraction and Hg-intrusion micromeritics.The experimental results indicate that wet-milling ultra-fine cement possesses high rheological properties and groutability.It can be filled densely in cracks of rock and hydrate fully,which may endow hydrated cement with high mechanical strength.Main hydration products of wet-milling ultra-fine cement are poorly crystalline C-S-H(Ⅰ),acicular AFt and plank-shape Ca(OH)_2.The dense crystal-network structure can be formed in the rock gaps filled with cement paste,but some weak regions exist owing to Ca(OH)_2.The features of micro-pore structure of hydrated wet-milling ultra-fine cement are few big harmful pores,abundant harmless micro pores and little most possible pore radius.

Mechanical Behaviors and Deformation Properties of Retaining Wall Formed by Grouting Mould-Bag Pile

The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.