Evaluation of pH and Compressive Strength Development of Alpha-Calcium Sulfate Hemihydrate-based Binder

알파형 반수석고 기반 결합재의 pH 및 강도발현 평가

Lee, Kyung-Ho;Yang, Keun-Hyeok

  • Received : 2015.11.26
  • Accepted : 2016.01.22
  • Published : 2016.02.20


This study examined the compressive strength development and pH values of alpha-calcium sulfate hemihydrate(${\alpha}-CH$)-based binders developed for vegetation concrete with neutral pH between 6~7. Considering cost down and strength enhancement of the prepared binders, the ${\alpha}-CH$ was partially replaced by ground granulated blast furnace slag(GGBS), fly ash(FA), or ordinary Portland cement(OPC) by 25% and 50%. The compressive strength of mortars using 100% ${\alpha}-CH$ was 50% lower than that of 100% OPC mortars. With the increase of the replacement level of GGBS or FA, the compressive strength of ${\alpha}-CH$-based mortars tended to decrease, whereas the pH values were maintained to be 6.5~7.5. The main hydration products of ${\alpha}-CH$-based binders with GGBS or FA were a gypsum($CaSO_4$), whereas portlandite($Ca(OH)_2$) was not observed in such binders. Meanwhile, the pH values of ${\alpha}-CH$-based binders with OPC exceeded 11.5 due to the formation of $Ca(OH)_2$ phase as a hydration product. From the thermogravimetric analysis, the amount of $Ca(OH)_2$ in ${\alpha}-CH$-based binders with OPC was evaluated to be approximately 10% of the cement content.


vegetation concrete;neutral pH;compressive strength;alpha-calcium sulfate hemihydrate;portlandite


  1. Shin SM. Life Cycle Assessment and Improvement of Green-roof Considering Materials for Maintenance [Master's thesis]. [Daejeon (Korea)]: Korea Advanced Institute of Science and Technology; 2008. 84 p.
  2. Kim JB, Cho HJ, Kim HY. Effects of Soil pH on the Growth and Antioxidant System in French Marigold(Tagetes patula L.). Korean Journal of Plant Resources. 2007 Aug;20(4):348-52.
  3. Zuo JH, Li JP, Yang F. Effects of Different Soil Types on the Panicle Traits and Yield Components of Northern Japonica Rice. Chinese Journal of Ecology. 2013;32(1):59-63.
  4. Han BH, Lee KJ. A Study on the Analysis of the Physiological Growth Condition and Improvement of Street Tree in Seoul. Korean Journal of Environment and Ecology. 1996;10(1):39-48.
  5. Park DC. Analytic Research about the Prediction of Long-term Neutralization Focused on the Reaction and Diffusion of Calcium Hydroxide. Journal of the architectural institute of Korea : Structure & construction. 2007 Aug;23(8):99-106.
  6. Choi KY. Development of Porous Concrete Blocks and Their Applicability Experiment for the Environment Favorable Consolidation of Rivers and Channels [Doctorate thesis]. [Seoul (Korea)]: Graduate School of Konkuk University; 2005. 204 p.
  7. Han CG, Kim JS, Hwang JH, Lee ST. Fundamental Properties of Planting Concrete on the Building Roof with the Kinds of Aggregate. Journal of the Architectural Institute of Korea: Structure & Construction. 2001;17(1):91-9.
  8. Korean Industrial Standards. Methods for Determination of pH of Aqueous Solutions [KS M 0011]. Seoul: Korean Agency for Technology and Standards. 2013, 8 p.
  9. Lee JH, Park CG, Park JS. Effect of Reinforcing Fiber on Mechanical Properties and Chemical Resistance of Porous Concrete with Hwang-toh. Journal of the Korean Society of Civil Engineers. 2011 Mar;31(2):105-13.
  10. Kim HH, Kim CS, Jeon JH, Park CG. Physical, Mechanical Properties and Freezing and Thawing Resistance of Non-Cement Porous Vegetation Concrete Using Non-Sintering Inorganic Binder. Journal of the Korean Society of Agricultural Engineers. 2014 Sep;56(5):37-44.
  11. Park SS, Ki KH, An HS, Park KK. Preparation of Calcium Sulfate ${\alpha}$-Hemihydrate from FGD Gypsum in the Autoclave. Applied Chemistry for Engineering. 2006;17(6):619-24.
  12. Korean Industrial Standards. Ground Granulated Blast-Furnace Slag for Use in Concrete [KS L 2563]. Seoul: Korean Agency for Technology and Standards. 2014, 8 p.
  13. Korean Industrial Standards. Fly Ash [KS L 5405]. Seoul: Korean Agency for Technology and Standards. 2016, 17 p.
  14. Korean Industrial Standards. Portland Cement [KS L 5201]. Seoul: Korean Agency for Technology and Standards. 2013, 13 p.
  15. Korean Industrial Standards. Methods of Testing Cement -Determination of Strength [KS L ISO 679]. Seoul: Korean Agency for Technology and Standards. 2011, 17 p.
  16. Korean Industrial Standards. Standard Test Method fro pH of Soil [KS F 2103]. Seoul: Korean Agency for Technology and Standards. 2013, 4 p.
  17. Korean Industrial Standards. Testing Method for Compressive Strength of Hydraulic Cement Mortars [KS F 2103]. Seoul: Korean Agency for Technology and Standards. 2012, 5 p.
  18. Kim MS, Jun YB, Lee CH, Oh JE. Use of CaO as an Activator for Producing a Price-Competitive Non-Cement Structural Binder Using Ground Granulated Blast Furnace Slag. Cement and Concrete Research. 2013;54:208-14.

Cited by

  1. Evaluation of Physiochemical Properties of Artificial Lightweight Soil Aggregates for Vegetation Produced from Hwang-toh Foamed Concrete vol.32, pp.10, 2016,
  2. Evaluation of Properties of Artificial Soil Aggregate Based on Ground Granulated Blast-Furnace Slag According to Unit Binder Content vol.20, pp.5, 2016,


Supported by : Ministry of Land, Infrastructure and Transport of Korean government