Effects of Sodium-Sulfate Addition on Consistency, Setting Time and Compressive Strength at Early Ages of Fly Ash-Cement Paste
The use of fly ash for concrete industry is gradually increasing owing to reducing CO2 emission from cement production, lowering the construction cost, and enhancing compressive strength at the late ages and durability of concrete.However, strength of fly-ash concrete is sometimes lower than that of normal concrete containing no fly ash.To overcome this drawback, several methods have been suggested, such as the use of a low water-to-cementitious materials ratio (w/cm) and an activation on pozzolanic reaction of fly ash by using alkali or sulfate activators.An activation by using 4% sodium sulfate (Na2SO4) as an activator, on the fly ash-cement pastes with low w/cm was carried out to assess the effectiveness of this activation on fresh properties and compressive strength at early ages of the pastes.In this study, Portland cement and low-calcium fly ash were used as cementitious materials.The pastes were prepared with two low w/cms of 0.30 and 0.35.The replacement ratios of cement by fly ash were 0, 20, and 40% by mass.The pastes were mixed in a mechanical mixer and cast in 50-mm-per-side cube-shaped molds.The consistency and setting time of the fresh pastes were measured by flow table test and Vicat apparatus, respectively.All specimens were demolded 24 h after casting and cured at temperature of 29±1 ℃ and relative humidity of 90±5%, which are nearly the same as the practical curing condition for concrete structures, until the designated test ages.Compressive strengths of the pastes were tested at 1, 3, 7, and 28 days.Results show that fly ash reduced the flow diameter of the fresh pastes but extended their setting time including initial and final setting times regardless ofw/cm and the addition of Na2SO4.Meanwhile, the addition of Na2SO4 increased slightly the flow diameter of the fresh pastes but shortened their setting time regardless of w/cm and fly-ash replacement.The higher the replacement of cement by fly ash, the lower the compressive strength of the pastes.The addition of Na2SO4 increased the compressive strength of the pastes at early ages (i.e., at 1, 3, and 7 days) and accelerated their strength development regardless of fly-ash replacement.Consequently, the addition of Na2SO4 not only increased slightly the consistency of the fresh pastes containing fly ash and shortened their setting time but also accelerated the strength at the early ages of the hardened fly ash-cement pastes.
Activation Compressive strength Cement paste Fly ash Sulfate
P.T.Bui A.K.Nguyen N.H.Nguyen Y.Ogawa K.Kawai
Department of Construction Materials, Ho Chi Minh City University of Technology, Ho Chi Minh City,Vi Department of Civil and Environmental Engineering, Hiroshima University, Higashi-Hiroshima, Japan
国际会议
福州
英文
335-342
2018-11-04（万方平台首次上网日期，不代表论文的发表时间）