Low-cement high-strength concrete with partial replacement of Portland cement with stone powder and silica fume designed by particle packing optimization

Abstract

Sustainability has become a major focus of the concrete industry, which is largely due to the CO2 emissions associated with Portland cement production. The process of crushing rocks to produce aggregates can also cause environmental damage since it generates stone powder, which is disposed of in the environment as waste material. Therefore, replacing cement with stone powder to reduce CO2 emissions during concrete production is an attractive alternative to sustainability. The use of high-strength concrete (HSC) appears to be another alternative since higher compressive strength results in lower CO2 emissions per MPa. In this context, the objective of the present work is to design a low-cement HSC via the partial replacement of Portland cement with stone powder and silica fume optimized using particle packing methods. The design approach selected consists of first designing the paste, followed by the design of the granular skeleton. Concretes were produced by varying the paste contents from 27 to 37% and the water/fines (w/f) ratio from 0.28 to 0.40. The efficiency of the HSCs was measured in the context of sustainability in terms of cement consumption and CO2 emissions, in addition to the properties of the fresh and hardened states. Results show that the most efficient composition of the paste was 64% Portland cement, 16% silica fume and 20% stone powder. The aggregate composition of 47% limestone sand, 30% gravel with a maximum particle size of 9.5 mm and 23% gravel with a maximum particle size of 19 mm presented the lowest void index. Respecting these material proportions, some concretes were designed with a compressive strength of 104 MPa using only 288 kg/m3 of cement. This represents a consumption of only 2.8 kg of cement/MPa of concrete compressive strength, which is less than the consumption reported by the literature for HSC (∼5 kg/m3/MPa) and results in a CO2 emissions/MPa reduction of over 44% in relation to concrete produced using mix design methods described in the literature. Furthermore, all of the low-cement HSC studied here presented high workability, excellent quality (according to the ultrasonic pulse velocities (above 4500 m/s)) and insignificant corrosion risk (based on the electrical resistivity test (higher than 100 KΩcm)). These findings contribute to the production of sustainable concretes since waste material can be used while simultaneously reducing greenhouse gas emissions.