Construction and Building Materials

An international journal dedicated to the investigation and innovative use of materials in construction and repair

Construction and Building Materials provides an international forum for the dissemination of research and development in the field of constructionand building materials and their application in new works and repair practice. The journal publishes a wide range of research and application papers which describe laboratory and numerical investigations or report on full scale projects.Construction and Building Materials also publishes detailed case studies and review articles, as well as short communications and discussions.

The materials and technology covered include: cement, concrete reinforcement, bricks and mortars, additives, corrosion technology, ceramics, timber, steel, polymers, glass fibres, recycled materials and by-products, sealants, adhesives.

The scope of Construction and Building Materials includes, but is not restricted to, new works and repair and maintenance of the following:bridges, high-rise buildings, dams, civil engineering structures, silos,highway pavements, tunnels, water containment structures, sewers,roofing, housing, coastal defences.

At a time when the pressure is on all engineers, architects and contractors to optimise use of new materials and up-to-date technologies,Construction and Building Materials provides essential information that will help improve efficiency, productivity and competitiveness in world markets. It is therefore vital reading for all professionals and academics involved with research into, or specification of, building materials.

Author duties: Acceptance of a manuscript for publication in the journal carries with it an understanding that the author, when requested, will fulfil an obligation to contribute their expertise to the review of others' manuscripts. Authors who are unwilling to assist with the review of a colleague's paper may in extreme cases find that their manuscripts are no longer welcomed for publication in Construction and Building Materials.

Abstract

Cement is the most energy-consuming component of concrete, leading to a high CO₂ release during its fabrication. Therefore, a reduction of the cement amount used in concrete mixtures would be beneficial from an environmental point of view. One way to do this is by replacing cement with a suitable material; in this research, recycled concrete fines obtained from crushed concrete (RCF) is used to replace part of the cement in new mortar recipes. RCF subjected to various thermal treatments were used to replace part of the cement in the standard mortar samples containing either OPC or slag- or fly-ash blended cements. Both untreated and thermally-treated RCF were characterized in terms of density, PSD, composition (XRF and XRD, as well as SEM), calorimetric behavior and mechanical strength when added into mortars. Mortar samples were tested and the results show that RCFs can be a beneficial addition, especially in the case of blended cements.

Particle size distributions of crushed material from the novel crusher SC 1 (SC 1 output) on a logarithmic scale, compared to the initial concrete solids mix (initial mix). The sieving size of 150 μm used for obtaining the RCF fraction is also marked on the graph.

Fig. 2. TG (% mass loss) and DTG (% mass loss/min) curves of the RCF sample, together with its DSC signal curve (μV/mg) for a heating treatment up to 1000 °C.

Fig. 3. Particle size distributions of thermally treated (110–800 °C) hardened cement paste samples, all subjected to the same grinding procedure.

Fig. 4. Particle size distributions of all binder materials used in this research: untreated (RCF-20) and thermally treated recycled concrete fines at different temperatures between 500 and 1100 °C. The cement, fly ash and slag employed in the study are included for comparison.

Fig. 5. XRD of reference RCF-20 and thermally treated RCF at 500 °C and 800 °C. A gravel sample used in the initial concrete mix was measured by XRF to contain 98% SiO₂ and is included for comparison. α-Quartz (▴); C₂S (○); portlandite (●); calcite (■); and lime (△).

Fig. 6. SEM images of untreated RCF-20 (a and b), 500 °C-treated RCF (c and d) and 800 °C-treated RCF (e and f) at the magnification of 5000×

Fig. 7. Calorimetric curves of RCF-20, 500 °C-treated RCF (RCF-500) and 800 °C-treated RCF (RCF-800) in a mix with water (a and b), as 10% cement replacement (c) and as cement replacement in a slag-cement mix (d). Measurements up to 72 h.

Fig. 8. Final spread of standard fresh mortars (after addition of SP for certain samples, as explained in Section 5): reference (where the binder is CEM I 42.5 N) and 10%, 20% and 30% replacement of the cement by RCF-20, RCF-500 and RCF-800 by mass.

Fig. 9. a. Mechanical properties of standard mortars: reference (where the binder is CEM I 42.5 N) and 10%, 20% and 30% replacement of the cement by fly ash, RCF-20, RCF-500 and RCF-800 by mass. (a) 7 days flexural strength, (b) 7 days compressive strength, (c) 28 days flexural strength, and (d) 28 days compressive strength.

Fig. 10. (a) 7 days and 28 days flexural strength of the reference, 10% 800 °C-treated RCF + 10% fly ash, 20% 800 °C-treated RCF and 20% fly ash replacement mortars. (b) 7 days and 28 days compressive strength of the reference, 10% 800 °C-treated RCF + 10% fly ash, 20% 800 °C-treated RCF and 20% fly ash replacement mortars.

Fig. 11. 7 days and 28 days compressive strength of slag-blended cement mortars, containing 70% slag + 20% CEM I + 10% RCF as binder.