High-Workability Concrete CE 165: Concrete Materials and Concrete Construction Introduction High- workability relates to both high consistency and high cohesiveness. Pioneering work by Japanese and German researchers during the 1980s has led to the development of high-workability concrete mixtures that are commercially known as self-compacting concrete. CE 165: Concrete Materials and Concrete Construction Self-compacting concrete Flowing-concrete that can be cast into place and can achieve de-aeration without the application of a vibrator, with no segregation and honey-combing CE 165: Concrete Materials and Concrete Construction Motivations The constructability of heavily congested reinforced concrete structures requires that the fresh concrete mixture should possess high fluidity. With the advent of superplasticizers, it is possible now to achieve values of the order of 200 to 250 mm without an increase in the water/cement ratio CE 165: Concrete Materials and Concrete Construction Potential problems Flowing concrete mixtures run the risk of bleeding, settlement, and segregation. Weak interfacial transition zone between cement paste and aggregate, as well as between cement paste and reinforcing steel. This risk becomes especially great with high placement heights, high shear rates in pumping, and excessive vibration during the consolidation of concrete. CE 165: Concrete Materials and Concrete Construction Japanese experience Reasons for the increasing demand of SCC in Japan: – a) complex shape of concrete structures and densely arranged bars make it more difficult to use a vibrator; – b) vibration compaction is noisy and deleterious to the health of construction worker, as well as an annoyance to people in the neighborhood; – d) in remote areas it is difficult to find skilled workers to carry out the compacting work at construction sites CE 165: Concrete Materials and Concrete Construction Materials and Mixture Proportions volume and maximum size of coarse aggregate must be controlled. Compared to conventional superplasticized concrete, which typically contains about 45% coarse aggregate and 25% fine aggregate (by absolute volume), SCC concrete mixtures are composed of approximately 25 to 30% coarse aggregate, 30-35% fine aggregate, and about 10% extra-fine particles (exclusive of cement). CE 165: Concrete Materials and Concrete Construction Materials -- Aggregate SCC the total volume of coarse and fine aggregate remains below 60% so that 40% or more of the volume consists of suspension (cement + extra-fine material + water + air). The maximum size of coarse aggregate is generally limited to a maximum of 20 mm. CE 165: Concrete Materials and Concrete Construction Japanese experience According to Nagataki and Fujiwara, in an experimental study when the volume of coarse aggregate was 24.5%, most concrete was able to pass through the reinforcing bars. When the volume of coarse aggregate was 34.5% concrete was unable to pass through the bars under all conditions. CE 165: Concrete Materials and Concrete Construction Materials High fluidity with relatively low water content is achieved by the use of a superplasticing admixture. Fly ash, ground blast-furnace slag, and limestone powder are normally used to provide the extra-fine particles other than cement; using cements alone would increase the cost and heat of hydration. CE 165: Concrete Materials and Concrete Construction Admixtures Commonly used viscosity-modifying agents in concrete include acrylic- or cellulose- based water-soluble polymers or polysacchrides of microbial sources, such as welan gum. Water-soluble polymers can imbibe some of the free water in the system, thus increasing the viscosity of the cement paste which, in turn, enables the paste to hold aggregate particles in a stable suspension. Incorporation of extra-fine materials in the SCC mixtures is not necessary if a viscosity-modifying agent is used. CE 165: Concrete Materials and Concrete Construction Viscosity-Modifying Agents Enhance the cohesion of the concrete. Minimize the accumulation of bleed water. Formulation: • Water-soluble synthetic or natural organic polymers with high molecular weight • Emulsions of several organic materials CE 165: Concrete Materials and Concrete Construction ESEM images of welan gum particles (scalebar is 100mm). (a) Dry particles at 70% RH (b) After 5 minutes at 100% RH (c) After 12 minutes at 100% RH Applications of ViscosityModifying Agents Underwater concrete Facilitates sufficient mobility of the concrete under water with little loss of cement. Self-compacting concrete Leads to high flowability with no segregation. Grouting Eliminates the migration of water from the grout due to the differential pressure. Helps maintain the cement particles in suspension once injection ceases. Applications The anchorage for a long bridge connecting the island of Honshi and Awajishima, bridge piers and high-rise buildings with dense steel reinforcement, stadiums with are complex in shape and where vibratory compaction is difficult. CE 165: Concrete Materials and Concrete Construction Coral Reef in Florida Keys CE 165: Concrete Materials and Concrete Construction Courtesy from Sam Yao Florida Keys CE 165: Concrete Materials and Concrete Construction One of the Ground Sites Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Damaged Coral Reef Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Applications In 1994, a ship ran aground at the Looe Key damaging over 1000 square meters and destroying 75 percent of the coral colonies. Underwater concrete was placed to stabilize the boulders and the surrounding reefs. Due to the sensitive environmental conditions at the site, the underwater concrete had to be flowable, but yet without causing turbidity and pollution in water. CE 165: Concrete Materials and Concrete Construction Repair Design Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Precast Repair Module Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Repair of Corral Reef in Florida Keys Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Setting a Precast Module Courtesy from Sam Yao CE 165: Concrete Materials and Concrete Construction Tremie CE 165: Concrete Materials and Concrete Construction Placement CE 165: Concrete Materials and Concrete Construction Concrete Delivery CE 165: Concrete Materials and Concrete Construction Washout test CE 165: Concrete Materials and Concrete Construction Details CE 165: Concrete Materials and Concrete Construction Placement CE 165: Concrete Materials and Concrete Construction Hydrostatic Balance Point CE 165: Concrete Materials and Concrete Construction CE 165: Concrete Materials and Concrete Construction Spacing CE 165: Concrete Materials and Concrete Construction Sequence CE 165: Concrete Materials and Concrete Construction Removal of Laitance CE 165: Concrete Materials and Concrete Construction CE 165: Concrete Materials and Concrete Construction CE 165: Concrete Materials and Concrete Construction CE 165: Concrete Materials and Concrete Construction Surface Coating and Painting 1) Vapor-barriers epoxy, asphalt 2) Latex (permeable) provides good adhesion CE 165: Concrete Materials and Concrete Construction
