Cellulose nanofibers synergizing with tannic acid enables high-performance grouting in deep geothermal environments

Achieving ultrahigh-flow grouting materials with sustained mechanical performance under deep geothermal conditions remains critical in underground engineering. This study explores a cellulose nanofibers -tannic acid synergistic modification method to enhance grout performance, overcoming the 'fast setting and low strength' dilemma in geothermal environments.. Through multi-scale characterization (fluidity,setting time,compression, hydration heat, XRD, FTIR, TG/DTG, MIP, SEM-EDS, Zeta Potential , Particle Size Distribution), the effects of cellulose nanofibers dosage, temperature, and curing age on the working performance, mechanical properties, composition and microstructure were investigated.The results show that the cellulose nanofibers synergizing tannic acid significantly inhibit the performance deterioration caused by high temperature. The interaction between tannic acid and hydroxyl groups on cellulose nanofibers constructs hydrogen-bond network, enhancing initial fluidity by 50% (up to 252 mm) and 7-day compressive strength by 19.24% (up to 31.5 MPa). And this network structure reduces the water loss rate caused by high temperature, the hydration products are oriented in 1μm pores through heterogeneous nucleation site regulation and bridging effect to form gradient densification structure. The optimal dosage of cellulose nanofibers to tannic acid (0.1% CNFs + 0.18% TA) was determined by multi-objective co-optimization. Based on the validation of ASTM C1437 standard, the dosage resulted in a 33.4% increase in 60-minute fluidity and a 26.41% enhancement in 7-day mechanical properties of the grouting material. The research results provide a theoretical paradigm and industrial benchmark for the design of grouting materials in deep engineering, which can support the demand of engineering practice under high temperature and high pressure environments.