International Concrete Abstracts Portal

Thermal insulation and thermal energy storage are becoming more and more attractive for residential and industrial buildings due to the need of sustainable development. The economical and efficient technique that can be used to produce building products for insulation and store energy is also the subject of research for a long time. Cement-based products manufactured by extrusion technique offer advantages in terms of the flexibility of section profiles, material performance enhancement and mass production mode. Different fillers can be used to achieve desired effects on thermal, mechanical and physical characteristics during extrusion process. These fillers include sand and expanded perlite which are good at thermal insulation and phase change composites which can provide high energy storage capacities. It is foreseeable that extruded building products with suitable fillers have potentiality for economical applications for thermal insulation and thermal storage of different kinds of buildings.

The design versatility of cement-based composites continues to make them attractive for a variety of specialized applications. Advanced processing techniques, including the Hatschek process, extrusion, self-consolidating concrete and slipform-cast concrete paving, offer great promise for improving innovation in the modern construction world. However, to advance the state-of-theart of cement-based products, the fresh state characteristics of these materials need to be well understood. Processing has a significant impact on composite performance, affecting fresh and hardened state properties as well as overall cost. In spite of its importance, relatively little is known about the relationship between processing and composite performance. Recent work at the Center for Advanced Cement-Based Materials (ACBM), headquartered at Northwestern University, has focused on developing a better understanding of this critical relationship. The role of processing on composite performance has been examined for a variety of advanced processing techniques, including the Hatschek process, extrusion, self consolidating concrete and slipform-cast concrete paving. The results indicate that overall composite performance can be enhanced by controlling fresh state properties. This paper presents a review of these studies and discusses ongoing research to link composite performance to microstructural changes.

The paper discusses the variety of processes that are used to manufacture GFRC products. It also includes descriptions of how the processes have developed and the reasons for their development.

Typical demolding times of GFRC cast parts are typically 16 hours. This has limited the acceptance of GFRC, or any cement based product, into products requiring high volume production because of the high costs of multiple molds associated with a material chemistry with such long demolding times. This paper discusses a unique system utilizing Portland Type I cement, a fast setting cement and specially designed mixing equipment to process the material so that demolding times in the 1 to 2 hour range are possible. A conventional weight formula (128 pcf or 2048 kg/m3 ) and a lightweight formula (71 pcf or 1136 kg/m3) are available. For convenience, the formulas are supplied pre-blended.

Extruded high-performance fiber-reinforced cementitious composites (HPFRCC) offer a number of benefits over the materials currently used in residential construction, including improved strength, ductility and durability, increased design flexibility, improved safety in the event of natural hazards and greater affordability. Despite these benefits, the use of extruded HPFRCC is not widespread in North America. Current extruded HPFRCC are difficult to nail, requiring excessive force to nail and often cracking due to nailing stresses. Research at the Center for Advanced Cement-Based Materials (ACBM), headquartered at Northwestern University, has focused on developing nailable extruded composites. Using a previously developed test method, the nailing performance of extruded HPFRCC was evaluated and compared with commercial products. Existing cavity expansion- and fracture mechanics- based models were used to determine the material parameters required for nailing. The results indicate that by tailoring both the matrix and the fiber reinforcement, nailable extruded composites can be produced. Nailable extruded HPFRCC have a reasonably low density and compressive strength (to allow for nail penetration) and a high fracture toughness (to resist cracking due the nailing stresses).