The early 3-day compressive strength of PMM in cyclic curing was higher than in normal condition.. The reduced ratio of compressive strength the ratio by com-pressive strength in cyclic
Trang 1···
Abstract
Polymer modification was widely used to improve the properties of construction materials The concept of polymer modification for mortar and concrete was put forward 80 years ago It was known that the use of polymers for modification can greatly improve the strength, adhesion, resilience, impermeability, chemical resistance and durability properties of mortars and concrete In southern Vietnam, a tropical weather country, the environment was usually hot with high humidity The durability of mortar or concrete coating was reduced over time in such a condition This study examines the strength of polymer-modified mortars in high temperature and high humidity Moreover, the results included the improvement of strength of acrylic emulsion polymer-modified mortar (PMM) by the addition of blast furnace slag Fifteen percent cement was replaced with blast furnace slag (BFS) in a mix proportion in order to improve strength of PMM The specimens were cured in cycles 50±2oC, RH 90±3%, for 5 hours and 20±2oC,
RH 60±3 %, for 19 hours per day The strength of PMM was measured at the age of 3, 7, 14, 21 and 28 days, 3 and 6 months and 1 year in a high temperature and high humidity cycles
Keywords: polymer-modified mortar, high temperature and high humidity cycles, blast furnace slag
···
1 Introduction
Cement mortar and concrete have some disadvantages such as
delayed hardening, low tensile strength, high drying shrinkage,
and low chemical resistance (Ohama, 1995) Polymer-modified
mortar has been investigated In modern concrete construction
and repair works the role of polymers was commonly used
(Chandra, 1994) The properties of polymer-modified mortar
depend on the type of polymer, the polymer-cement ratio, the
water-cement ratio and the curing condition Previous researches
on cement based mortar, polymer modified cement based
mortars and epoxy mortars have shown that some of these
materials did not perform well on hydraulic structures to satisfy
site and climatic condition (Ru, 2002)
Jenni et al (2006) had shown that there were reverse and
irreversible changes in microstructures and physical properties of
polymer-modified mortars during wet storage Hassan et al
reported that the compressive strength of polymer modified
concrete was slightly higher than normal concrete in a hot-dry
environment (Hassan, 2001) In the tropical countries, there were
two typical seasons: dry and rain In the summer time from May
to September, especially in southern Vietnam, the temperature
and humidity were usually very high (Information Center of
Natural Resources and Environment, MORE) Polymer-modified
mortars were used as the waterproof layer of structures and on the roof of buildings However, the quality of polymer-modified mortars was reduced after a short time Improving the strength of polymer-modified mortar in high temperature and high humidity was the main focus in this study
2 Experiment
2.1 Materials
An ordinary portland cement was used in this study The specific gravity was 3.15 g/cm3
and the Blaine’s specific area was 3,180 cm2
/g The initial setting time was about 170 minutes and the finishing setting time was more than 7 hours
The particle size analysis of fine aggregate was described in Fig 1 The specific gravity of fine aggregate was 2.65 g/cm3
Two kinds of acrylic emulsion polymer (AE) were used in this study were described in Fig 2 and Table 1
Blast furnace slag (BFS) was used in this study with 15% by weight of cement in mix proportion Properties of BFS were described in Table 2
2.2 Test program The mixing time was 150 seconds Specimens, 50×50×50 mm, were prepared for compressive tests (ASTM C 109/C 109M)
*Member, Professor, Dept of Civil Engineering, Yeungnam University, Gyeongsan 712-749, Korea (E-mail: hmkwon@yu.ac.kr)
**Lecturer, Dept of Civil Engineering, Ho Chi Minh City University of Technology, Vietnam (Corresponding Author, E-mail: nnthuy@hcmut.edu.vn)
***Doctoral Student, Dept of Civil Engineering, Yeungnam University, Gyeongsan 712-749, Korea (E-mail: tuanmaterial@yahoo.com)
Trang 2Specimens, 50 mm diameter and 100 mm height were prepared
for splitting tensile tests (ASTM C496-96) Specimens, 40×40×
160 mm, were prepared for the flexural tests (ASTM C 348-97)
After the specimens were casted, they were cured at 20±2o
C and
RH 60±3% for 1 day After 1 day, the specimens were cured in a
cyclic condition: 5 hours at 50±2o
C and RH 90±%; 19 hours at 20±2o
C and RH 60±3% The graph of temperature for the cyclic
curing conditions was shown in Fig 3
2.3 Mix Proportion
In this study, the sand-cement ratio was 3:1, the water-cement
ratios were from 0.30 to 0.50 The polymer-cement ratios were:
5, 10, 15 and 20% (Table 3)
Fig 1 Sieve Analysis of Sand
Fig 2 Molecular Formula of Acrylic Emulsion Polymer
Table 1 Properties of Acrylic Emulsion Polymer
Parameter AE2 AE1
Type 1 Type 2 Type 3
Mw 1038744 122828608 1790754 390237
Density (g/cm3
Total solids (%) 53 52
Appearance Milky white Milky white
Table 2 Properties of Blast Furnace Slag
Bulk density (kg/m3
Fineness (cm2/g) 4,350
Activity index (%) 7 days 97
28 days 112
Fig 3 Temperature for the Cyclic Curing Conditions
Table 3 Mix Proportions Code w/c (%)p/c s : b b (%) Curing condition
c BFS UM050d 0.50 0 3 : 1 100 0 20±2, RH 60% UM050h2 0.50 0 3 : 1 100 0 Cycle UM0050BFS 0.50 0 3 : 1 85 15 Cycle AE-0535d 0.35 5 3 : 1 100 0 20±2, RH 60% AE-0535h2 0.35 5 3 : 1 100 0 Cycle AE-0535BFS 0.35 5 3 : 1 85 15 Cycle AE-0540d 0.40 5 3 : 1 100 0 20±2, RH 60% AE-0540h2 0.40 5 3 : 1 100 0 Cycle AE-0540BFS 0.40 5 3 : 1 85 15 Cycle AE-1030d 0.30 10 3 : 1 100 0 20±2, RH 60% AE-1030h2 0.30 10 3 : 1 100 0 Cycle AE-1030BFS 0.30 10 3 : 1 85 15 Cycle AE-1035d 0.35 10 3 : 1 100 0 20±2, RH 60% AE-1035h2 0.35 10 3 : 1 100 0 Cycle AE-1035BFS 0.35 10 3 : 1 85 15 Cycle AE-1527d 0.27 15 3 : 1 100 0 20±2, RH 60% AE-1527h2 0.27 15 3 : 1 100 0 Cycle AE-1527BFS 0.27 15 3 : 1 85 15 Cycle AE-1530d 0.30 15 3 : 1 100 0 20±2, RH 60% AE-1530h2 0.30 15 3 : 1 100 0 Cycle AE-1530BFS 0.30 15 3 : 1 85 15 Cycle AE-1535d 0.35 15 3 : 1 100 0 20±2, RH 60% AE-1535h2 0.35 15 3 : 1 100 0 Cycle AE-1535BFS 0.35 15 3 : 1 85 15 Cycle AE-2025d 0.25 20 3 : 1 100 0 20±2, RH 60% AE-2025h2 0.25 20 3 : 1 100 0 Cycle AE-2025BFS 0.25 20 3 : 1 85 15 Cycle AE-2035d 0.35 20 3 : 1 100 0 20±2, RH 60% AE-2035h2 0.35 20 3 : 1 100 0 Cycle AE-2035BFS 0.35 20 3 : 1 85 15 Cycle AE-2040d 0.40 20 3 : 1 100 0 20±2, RH 60% AE-2040h2 0.40 20 3 : 1 100 0 Cycle AE-2040BFS 0.40 20 3 : 1 85 15 Cycle p: polymer; w: water, c: cement, s: sand; b: binder; BFS: blast furnace slag; UM: Unmodified mortar; d: curing 20±2o
C, RH 60±3%; h2: cyclic curing conditions
Trang 3Fig 4 Trend of Compressive Strength of Acrylic PMM with Different Curing Conditions Table 4 Compressive Strength of Acrylic PMM with Different Curing Conditions
Code
Compressive strength (MPa)
Code
Compressive strength (MPa) 3
days
7 days
14 days
21 days
28 days
90 days
180 days
1 year
3 days
7 days
14 days
21 days
28 days
90 days
180 days
1 year UM050d 16.8 21.7 28.4 32.0 33.4 34.9 35.6 36.2 UM050h2 19.1 24.6 30.3 33.0 34.3 35.1 35.7 35.9 AE1-0535d 19.0 26.5 33.5 36.7 37.8 39.8 41.0 41.5 AE2-0535d 19.2 26.7 33.5 36.4 37.1 38.9 40.2 41.0 AE1-0535h2 19.7 26.0 32.1 34.7 35.6 36.5 37.2 37.4 AE2-0535h2 20.1 27.0 32.4 34.6 35.2 35.8 36.7 37.2 AE1-0540d 19.6 26.2 32.2 35.1 36.4 38.4 39.0 39.6 AE2-0540d 20.0 27.2 34.0 37.1 38.0 40.1 41.3 41.9 AE1-0540h2 19.9 25.3 30.5 32.9 33.8 34.8 35.1 35.5 AE2-0540h2 20.5 26.6 32.3 35.0 35.6 36.6 37.5 37.9 AE1-1030d 19.6 27.4 34.1 37.4 38.5 40.6 41.3 42.1 AE2-1030d 21.0 27.4 34.3 37.5 38.7 40.8 42.0 42.9 AE1-1030h2 20.4 27.0 32.8 35.4 36.0 37.2 37.6 38.0 AE2-1030h2 22.1 27.8 33.3 35.8 36.7 37.7 38.6 39.2 AE1-1035d 20.4 28.6 36.5 40.1 41.0 43.2 44.1 44.7 AE2-1035d 21.5 28.6 35.9 39.1 40.6 42.7 43.4 43.8 AE1-1035h2 20.7 27.8 34.6 37.5 38.0 39.0 39.5 39.8 AE2-1035h2 22.1 28.0 34.1 36.8 37.8 38.8 39.2 39.4 AE1-1040d 19.3 25.6 32.7 35.8 36.6 38.7 39.3 39.8 AE2-1040d 19.5 27.2 33.8 36.6 37.5 39.2 40.1 40.8 AE1-1040h2 18.8 24.3 30.6 33.1 33.5 34.8 34.9 35.2 AE2-1040h2 19.2 26.0 31.8 34.1 34.5 35.4 35.8 36.3 AE1-1527d 23.0 30.7 37.6 40.8 42.3 44.8 46.1 46.8 AE2-1530d 21.5 29.8 37.2 40.0 41.2 43.3 44.2 45.3 AE1-1527h2 23.8 29.5 35.6 38.2 39.3 40.7 41.3 41.6 AE2-1530h2 22.4 29.2 35.4 37.8 38.6 39.3 39.8 40.5 AE1-1535d 19.5 26.8 33.0 35.5 36.2 37.8 38.7 39.6 AE2-1535d 20.4 27.3 35.2 38.6 39.7 41.3 42.0 42.6 AE1-1535h2 19.0 25.6 30.8 32.8 33.2 33.9 34.4 34.9 AE2-1535h2 20.0 26.3 33.0 35.8 36.8 37.3 37.6 38.0 AE1-1540d 17.2 22.6 28.3 30.8 31.4 32.7 33.3 34.2 AE2-1540d 18.3 26.0 32.8 35.3 36.2 37.8 38.5 39.1 AE1-1540h2 16.4 21.3 26.2 28.2 28.5 29.1 29.3 29.8 AE2-1540h2 17.6 24.7 30.6 32.6 33.1 33.8 34.1 34.5 AE1-2024d 21.5 28.2 34.8 38.1 39.6 41.7 43.3 43.9 AE2-2030d 21.1 29.3 35.5 38.0 38.5 40.4 41.3 42.2 AE1-2024h2 21.1 27.1 32.9 35.6 36.7 37.6 38.7 38.9 AE2-2030h2 20.7 28.1 33.3 35.4 35.8 36.4 36.8 37.3 AE1-2035d 16.3 21.7 27.6 30.1 31.0 32.2 33.0 33.3 AE2-2035d 18.3 23.8 29.8 32.5 33.4 34.5 35.0 35.5 AE1-2035h2 15.6 20.4 25.4 27.3 28.0 28.5 29.0 29.1 AE2-2035h2 17.7 22.5 27.6 29.7 30.4 30.9 31.2 31.5 AE1-2040d 14.6 19.9 24.7 26.5 27.4 28.4 29.0 29.4 AE2-2040d 15.7 21.2 26.5 28.7 29.4 30.5 31.0 31.4 AE1-2040h2 13.7 18.4 22.4 23.9 24.6 24.9 25.2 25.4 AE2-2040h2 14.9 19.8 24.4 26.1 26.6 27.0 27.3 27.5
Trang 4modified mortar (Table 4) because too much water was used for
hydrating the cement
The early 3-day compressive strength of PMM in cyclic curing
was higher than in normal condition However, the later
compressive strength of PMM in cyclic curing condition was
lower than PMM in normal condition (Fig 4)
The reduced ratio of compressive strength (the ratio by
com-pressive strength in cyclic curing conditions to the comcom-pressive
strength for normal condition) was changed adversely according
to the age of PMM The reduced ratio was found to be more than
1.0 in the first few days when p/c was from 5% to 10% When
the ages of PMM were over 7 days, the reduced ratio was less than 1.0 and decreased with curing time The higher the p/c was, the higher the reduced ratio was (Fig 5)
3.2 Tensile Strength The results of tensile strength of acrylic PMM were shown in Figs 6 and 7
The tensile strength of unmodified mortar in cyclic curing conditions was higher than in the normal condition during the first 3 days after casting but, beyond the age of one week, the strength changed slowly
Fig 5 Reduced Ratio of Compressive Strength of PMM in High Temperature and High Humidity
Fig 6 Trend of Tensile Strength of Acrylic PMM with Different Curing Conditions
Fig 7 Reduced Ratio of Tensile Strength of PMM in High Temperature and High Humidity
Trang 5The results of flexural strength of PMM were shown on Figs 8
and 9 Similar to the results of compressive strength and tensile
strength, Fig 8 showed that the flexural strength of unmodified
mortar in curing cycles was higher than in normal condition
during the first 3 days after casting but, over the age of one week,
the situation changed slowly After 6 months, the flexural
strengths of specimens for both curing conditions were nearly
the same
The early 3-day flexural strength of PMM in cyclic curing
condition was higher than 3-day early flexural strength of PMM
in normal condition However, the later flexural strength of
PMM in cyclic curing condition was lower than PMM for
normal condition
The reduced ratio of flexural strength (the ratio by flexural
It was observed that increasing the temperature of curing will speed up the chemical reactions of hydration and thus it has beneficial effects to the early strength of mortar or concrete Although a higher temperature during placing and setting increases the very early strength, it may adversely affect the strength from about 7 days onwards The explanation was that a rapid initial hydration appears to form products of a poorer physical structure, probably more porous, so that a proportion of the pores will always remain unfilled (Neville, 1996)
In polymer-modified mortar, both cement hydration and poly-mers phase formation by the coalescence of polymer particles proceed well to yield a monolithic matrix phase with a network structure in which the cement hydrate phase and polymer inter-penetrate into each other, and aggregates were bound by such a
Fig 8 Trend of Flexural Strength of Acrylic PMM with Different Curing Conditions
Fig 9 Reduced Ratio of Flexural Strength of PMM in High Temperature and High Humidity
Trang 6co-matrix phase (Tobing, 2000) The strength of
polymer-modified mortar was affected by various factors that tend to
interact with each other: the natural materials, the control factors
for mix proportions, curing method and testing method Under
hot-dry curing condition, polymer and polymer modified repair
materials exhibit improved strength, permeability, diffusion and
shrinkage properties when compared to conventional cementitious
repair mortars (Hassan, 2000) However, Mirza et al showed
that the wet curing condition had an adverse effect on the
com-pressive strength of polymer-modified mortar (Mirza, 2002)
Acrylic latex polymers were made from copolymer of acrylates
or methyl acrylates with irregular structure This irregular
struc-ture prevents the co-location order of polymer chains and forms
a tough, flexible polymer with both elasticity and plasticity Thus, long-term exposure to heat and light should first induce thermal degradation or photolysis of ester radicals and methyl on the side chain, then irregular rupture of molecular groups on the main chain would subsequently occur (Ding, 2006)
The decreasing strength of polymer-modified mortar in high temperature and high humidity was very clear The strength decreased from 9% to 14% (Figs 5, 7 and 9) The results show that high temperature and high humidity has an adverse effect on the strength of polymer-modified mortar
3.4 Improvement of the Strength Fifteen percent by weight of cement was replaced by BFS in
Table 5 Compressive Strength of PMM with and without BFS in Cyclic Curing Conditions
Code
Compressive strength (MPa)
Code
Compressive strength (MPa) 3
days
7 days
14 days
21 days
28 days
90 days
180 days
1 year
3 days
7 days
14 days
21 days
28 days
90 days
180 days
1 year UM0050h2 19.1 24.6 30.3 33.0 34.3 35.1 35.7 35.9 UM0050BFS 18.0 23.7 29.7 33.1 34.9 36.0 36.6 37.1 AE1-0535BFS 18.6 24.8 31.9 35.7 37.1 38.4 39.3 40.1 AE2-0535BFS 19.4 26.8 33.3 35.8 36.7 38.5 39.2 39.8 AE1-0535h2 19.7 26.0 32.1 34.7 35.6 36.5 37.2 37.4 AE2-0535h2 20.1 27.0 32.4 34.6 35.2 35.8 36.5 37.2 AE1-1030BFS 19.4 26.8 33.6 36.4 37.8 39.3 40.4 41.2 AE2-0540BFS 20.3 26.3 33.3 35.9 37.2 38.7 39.5 40.3 AE1-1030h2 20.4 27.0 32.8 35.4 36.0 37.2 37.6 38.0 AE2-0540h2 20.5 26.6 32.3 35.0 35.6 36.6 37.5 37.9 AE1-1035BFS 21.5 28.6 35.4 37.9 38.5 40.6 42.0 42.9 AE2-1035BFS 21.8 27.8 35 38.9 40.5 41.6 42.2 42.9 AE1-1035h2 20.7 27.8 34.6 37.5 38 39.0 39.5 39.8 AE2-1035h2 22.1 28.0 34.1 36.8 37.8 38.8 39.2 39.4 AE1-1527BFS 22.5 30.1 37.0 40.1 41.5 43.0 44.1 44.8 AE2-1530BFS 22.0 29.1 36.4 40.2 41.9 43.2 44.9 45.5 AE1-1527h2 23.8 29.5 35.6 38.2 39.3 40.7 41.3 41.6 AE2-1530h2 22.4 29.2 35.4 37.8 38.6 39.3 40.0 40.5 AE1-1535BFS 18.4 24.9 31.0 34.0 35.6 37.2 38.1 38.8 AE2-1535BFS 19.6 26.0 33.7 37.5 39.0 40.3 41.1 41.4 AE1-1535h2 19.0 25.6 30.8 32.8 33.2 33.9 34.4 34.9 AE2-1535h2 20.0 26.3 33.0 35.8 36.8 37.3 37.6 38.0 AE1-2024BFS 20.9 27.6 34.2 37.5 39.0 40.4 41.6 42.3 AE2-2025BFS 21.9 28.2 35.0 38.5 40.0 42.4 43.5 44.2 AE1-2024h2 21.1 27.1 32.9 35.6 36.7 37.6 38.7 38.9 AE2-2025h2 22.1 28.6 34.9 37.2 38.0 38.6 39.6 40.0 AE1-2035BFS 15.1 20.1 25.7 28.6 29.9 30.8 31.5 31.9 AE2-2035BFS 17.2 22.3 28.2 31.0 31.9 32.6 33.0 33.6 AE1-2035h2 15.6 20.4 25.4 27.3 28.0 28.5 29.0 29.1 AE2-2035h2 17.7 22.5 27.6 29.7 30.4 30.9 31.2 31.5
Fig 10 Compressive Strength of PMM with and without BFS in Cyclic Curing Conditions
Trang 7mix proportion to improve the compressive strength of PMM
(Table 5; Fig 10) When 15 % cement was replaced by BFS, the
early age of compressive strength of PMM containing BFS (fill
color markers in Fig 10) was lower than the early age of
compressive strength of PMM without BFS (un-fill color
markers in Fig 10) The compressive strength of PMM with
BFS was nearly the same without BFS at 14 days However,
after 14 days in cyclic curing conditions, the compressive
strength of PMM with BFS was higher than PMM without BFS
(Fig 10, focus parts) The development of tensile strength and
flexural strength was similar to compressive strength The early
age of tensile strength and flexural strength of PMM containing
BFS were lower than PMM without BFS in cyclic curing
conditions The development of later age of tensile/flexural
strength of PMM containing BFS was higher than PMM without
BFS The significant effect of BFS on tensile/flexural strength of
PMM was observed (Table 5; Figs 11 and 12)
The improved ratios (ratio by strength of PMM with BFS to
the strength of PMM without BFS) of 15% polymer (series
AE-15BFS) and 20% polymer (series AE-20BFS) were higher than
for the 5% polymer (series AE-05BFS) and 10% polymer (series
AE-10BFS) The improved ratio of PMM was higher than the
unmodified mortar (Figs 13, 14 and 15) The improved ratio of PMM with BFS increases over time In this study, the improved ratio of PMM with BFS increased from 8 to 12% When BFS was used instead of cement, it was for the purpose of increasing SiO2 The molecular density of SiO2 was increased so that it was easy to have the electric bond and ionic bond between SiO2 and positive ions Ca2+
and polymer molecular (Ohama, 1995) The
Fig 11 Tensile Strength of PMM with and without BFS in Cyclic Curing Conditions
Fig 12 Flexural Strength of PMM with and without BFS in Cyclic Curing Conditions
Fig 13 Improved ratio of Compressive Strength of PMM with BFS in Cyclic Curing Conditions
Trang 8aggregate surface bonding was increased by the reaction of SiO2
and Ca2+
and polymer molecules Moreover, the fineness of BFS
was very small, so that they were able to fill the pores in the
structure of PMM
4 Conclusions
• High temperature and high humidity has an adverse effect on
the strength of polymer-modified mortar The strength of
poly-mer-modified mortar in cyclic curing conditions was lower
than for normal condition The strength of polymer-modified
mortar in cyclic curing conditions increased less than in normal
condition after 28 days
• The strength of PMM in cyclic curing conditions was higher
than for normal condition at first 3 days The reduced ratio
between the strength of polymer-modified mortar of specimens
in cyclic curing conditions and in normal condition depended
on the polymer-cement ratio in mix proportions It decreases over time The higher the polymer ratio was used, the lower reduced ratio was observed
• The replacement of 15% cement by BFS can improve the strength of PMM in high temperature and high humidity The improved ratio of PMM with BFS was higher than for the unmodified mortar with BFS The improved ratio of PMM with BFS increased over time
• BFS improved the strength of PMM from 8 to 12%
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Fig 14 Improved Ratio of Tensile Strength of PMM with BFS in
Cyclic Curing Conditions
Fig 15 Improved Ratio of Flexural Strength of PMM with BFS in
Cyclic Curing Conditions