Kaolinite plastic binder in mortars: Rheological and mechanical properties

Abstract

Portland cement and hydrated lime-based mortars are widely used in civil construction for covering and laying walls, sealing or structural restoration. However, the binders used in the production of mortar are produced in a way that is harmful to the environment, highlighting the need for alternative binders. In this work, the use of kaolinite plastic binder in mortars was evaluated, replacing hydrated lime with the material at levels of 0%, 50% and 100%. The importance of this study is to evaluate the feasibility of using an alternative binder in Portland cement and hydrated lime-based mortars. Fresh state properties were evaluated, such as consistency, squeeze flow and density in the fresh state; in addition to properties in the hardened state, such as compressive strength, water absorption, x-ray diffraction (XRD) and scanning electron microscopy (SEM). The characterization results of kaolinite plastic binder (D10 = 0.00009 mm and D60 = 0.0004 mm) show that the material has a particle size closer to hydrated lime (D10 = 0.00001 mm and D60 = 0.0004 mm), than Portland cement and quartz sand, evidenced by parameters D10 and D60. Additionally, the kaolinite plastic binder presents moderate pozzolanicity, indicating the feasibility of being used in this type of application. The workability tests show that kaolinite plastic binder has the potential to improve the workability of the mortar. In dynamic tests (consistency) it was observed that the 100% kaolinite plastic binder composition is viable as it promotes an increase in spread from 253 to 265 mm. In static tests (squeeze flow) the composition with 50% kaolinite plastic binder showed the best spreading results, with values of 10.7 mm, while the compositions containing 0% and 100% showed spreading of 8.97 and 7.40 mm, respectively. This demonstrates the potential for using kaolinite plastic binder in mortars. The hardened state results, such as compressive strength and water absorption, were also satisfactory. Although the compressive strength values showed a reduction with the use of kaolinite plastic binder, the values reached 7.5 MPa after 28 days, which is compatible with the proposed application. Finally, it was observed from the results of XRD and SEM that the kaolinite plastic binder shows adhesion with the hydration products of the Portland cement in the mortar, promoting a reduction in ettringite and portlandite due to its moderate pozzolanicity. Based on these results, it is possible to conclude that kaolinite plastic binder is a viable substitute for hydrated lime in mortars.