Relation between Porosity and Compressive Strength of Slag Concrete

1
Relation between Porosity and Compressive
Strength of Slag Concrete
An-Shun Cheng, Tsong Yen, Yu-Wen Liu, Yeong-Nain
Sheen
An-Shun Cheng is a Ph.D. candidate of Civil
Engineering at National Chung-Hsing University.
carat_at_ms47.url.com.tw Tsong Yen is a professor
of Construction Engineering at Chaoyang
University of Technology. tyen_at_dragon.nchu.edu.tw
Yu-Wen Liu is a professor of Civil and Water
Resources Engineering at National Chiayi
University. yuwen_at_mail.ncyu.edu.tw Yeong-Nain
Sheen is an associate professor of Civil
Engineering at Kaohsiung University of Applied
Sciences. sheen_at_cc.kuas.edu.tw
Test Variables
Mixture Proportions
Test Methods
kg/m3

• Cylinder specimen, ?100 x 200 mm
• for compression test. (ASTM C109)
• A Quantachrome PoreMaster mercury intrusion
• porosimeter (MIP) was used to measure the
  pore
• volume of concrete.
• ? The range of measured pore diameter was
• from 10 µm to 3.5 nm.

Results-Pore Structure and Compressive Strength
of Concrete
10070
7030
0.0718
W/B0.35
W/B0.50
W/B0.70
Table. Capillary pore volume(c.c/g)of concrete

• At early ages (1 to 7 days), the pore structure
  has a gradually change from
• larger capillary pore to smaller gel pore
  because of the cement hydration
• and pozzolanic reaction.
• At late ages (28 to 56 days), the capillary pore
  volume is obviously smaller.

• From 1 day to 7 days, the total pore volume of
  slag concrete is almost larger than that of plain
  concrete.
• The bigger the substitution ratio is, the
  larger the total pore volume will be.
• After 28 days, the total pore volume of slag
  concrete is almost smaller than that of plain
  concrete. It implies
• that the pozzolanic reaction of slag gets
  more apparent, and results in a strength
  enhancement.

• Adding 40 slag still has an advantage to the
  strength of concrete at late ages.

Results-Relation of Pore Parameters and
Compressive Strength

• The big capillary pore volume has the closest
  correlation with the compressive strength,
  and its R2 can reach to 0.926. It means that the
  big capillary pore volume has a most direct
  influence to the compressive strength.

• The R2 between the gel pore volume and strength
  is only 0.425. It represents that the existence
  of gel pores will not affect the strength, and
  this is because the size of gel pore is very tiny
  and the paths between gel pores is hard to
  through.

• The optimum pore parameter is big capillary pore
  volume.
• The relation equations ln(S) -20.887(B-Vc)3.8
  36

Table. The R2 between all pore parameters and
strength

• Conclusions
• Adding slag into concrete will improve the
  microscopic properties of paste, and the pore
  structure has a gradually change from larger
  capillary pore to smaller gel pore because of the
  cement hydration and pozzolanic reaction. So the
  capillary pore volume gradually decreases, the
  strengths of interfacial transition zone and
  paste therefore enhance.
• At early ages, the strength decreases apparently
  with the increase of substitution ratio of slag.
  After 28 days, the pozzolanic reaction gets
  apparent and the strength of slag concrete is
  higher than that of plain concrete.
• The big capillary pore volume has the closest
  correlation with the compressive strength, and
  its R2 can reach to 0.926.
• It means that the big capillary pore volume
  is the optimum pore parameter for predicting
  compressive srength.