by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Concrete In Australia : December 2013
30 Concrete in Australia Vol 39 No 4 FEATURE: RHEOLOGY content/limestone fillers. The extra cementitious content increases the cost (as in some countries the benefits of using fly ash/slag are not available in commercial terms) and in some pours the heat of hydration is also an issue. Add to this any requirement for re-tempering, the SCC would also pose immense problems in terms of mix stability/robustness of the mix. The excess of cement content, the extra amount of fines required for SCC requirement compliance and the logistics add costs to production. Hence, if one were to consider in terms of reducing total fines content and cement content without compromising on the properties of SCC, the ready mix industry and the specifiers could benefit on larger scale instead of restricting use of normal SCC in cases of high reinforcement congestion (in critical sections like columns-beams, girders/inaccessible areas). 2.0 EVOLUTION OF LF-SCC In the ready mix concrete application, traditional SCC has to be supplied by a ready mix producer with high cementitious content with a mandatory inclusion of crushed or natural fillers (<150μ). Any variations in the properties of fresh SCC are adjusted by changes effected in the cementitious contents (>450 kg/m3), the fines content (limestone fillers) as well the superplasticiser and/or viscosity modifying agent .4 A higher quantity of powder content causes an increase of pumping pressure and a decrease in finishing performance due to the high viscosity of concrete during placement. Concrete production costs may be enhanced in normal SCC applications with additional points in quality control at production and placement locations, apart from making arrangements for extra storage bins/silos. The innovative LF-SCC endeavours to achieve the fresh and hardened properties of SCC by reduction of total cementitious and/or fines content leading to an economical SCC which is referred to here as the LF-SCC. In all cases in this paper the comparison of LF-SCC is with respect to the traditional vibratable concrete (TVC), as the challenge is to convert the normal slump concrete (~100–125 mm slump) to SCC-like properties at approximately the same cementitious levels to achieve better economy and at the same time improve the paste quality in LF-SCC against the TVC. As a sustainable initiative, LF-SCC promotes the 3Es in the construction industry – Ecology, Economy and Ergonomy. Ecology – reduced cementitious fines (lower clinker factor) Economy – reduced vibration (energy) costs and lower manpower requirement to achieve similar or higher productivity Ergonomy – lesser noise during concrete placement at night and more comfort to placers for finishing concrete. 3.0 MEASURABLE PROPERTIES OF LF-SCC Like the measurable properties of traditional SCC (for example, slump flow, T500 and V-funnel time) LF-SCC is also measured on a similar trend. It is important to point out in the context of application that LF-SCC is preferred for R2 and R3 categories of reinforcement (as per JSCE recommendations) – typically for concrete sections where the reinforcing bar spacing is 60-200 mm or above. Traditional SCC is applicable for R1 category (heavily reinforced section having steel of 350 kg/m3) where grades of concrete, by default, are definitely higher than 45 MPa. It has been observed in many instances – in Japan, ASEAN countries, India and China – that LF-SCC prepared with special innovative synthetic VMA integrated within the superplasticiser has much better robustness in terms of cement compatibility and/or slight changes in water content. The superplasticiser with the incorporated synthetic VMA together offer perfect balance and stability against bleeding and segregation as shown in Figure 1, which shows yield values versus plastic viscosity.5 Figure 1: Yield value versus plastic viscosity – the balance in LF-SCC. With regard to the cost, low fines self-consolidating concrete in strength classes 25–40 MPa have shown marginal cost increase compared to TVC, but with a huge number of benefits as explained before in this paper. 4.0 EXAMPLES OF PROJECT WORK Japan These days a sustainable contribution6 to society is required in construction circumstances in Japan. In view of total construction cost considering shortening work periods, CO2 reductions, longer service life of structural object and improvement of worker’s safety, it is considered that SCC is extremely necessary and effective. Accordingly, a new air entraining agent (AE) and high-range water-reducing formulated polymerised viscosity enhancer agent was developed. The proposed technology can upgrade concrete of nominal strength 30–36 MPa to high fluidity concrete with self-compacting property economically and more easily without segregation (LF-SCC). Examples of construction results in Japan Application example 1 Work summary: • Construction name: Superstructure work of expressway at a river bridge (Kurosakigawa-bridge) • Contractee / Contractor: MLIT Hokuriku Regional Development Bureau / TEKKEN Corporation • Type: Rigid-frame-box-girder bridge with three spans • Design condition: Bridge length: 168 m (span:44.5m+76m+44.5m) • Design strength of concrete: 40 N/mm2. 29-35 Kar.indd 30 29-35 Kar.indd 30 25/11/13 2:56 PM 25/11/13 2:56 PM