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Properties of grc containing inorganic fillers
The International
Journal of Cement Composites
and Lightweight
Properties of grc containing inorganic fillers 6.Singh and A. J. Majumdar”
Concrete,
Volume 3, Number 2
May 1981
SYNPOSIS Some of the strength properties of grc containing four different types of fillers have been determined for composites kept in three different environments up to IO years. These environments were relatively dry air and water both at 20 “C, and natural weathering conditions at Garston. The non-pozzolanic fillers such as china claywaste or quarry fines acted as diluents to the cement thereby lowering those properties of the composite such as the limit of proportionality that are matrix dependent. The long-term strength of grc is not affected in a major way by the addition of these fillers although the initial strength values are lower than those of standard grc. The Italian pozzolana used in the study has given encouraging results. The grc composites containing this filler has given 26 MN/m* as the modulus of rupture and 5 KJ/m’ as the impact strength after continuous storage under water for ten years, The corresponding values for standard grc are 17 MN/m* and 2 KJ/m’ respectively. It is believed that the improved properties of the modified grc is due to the chemical reaction between the pozzolana and Ca++ and OH- produced by the hydrating cement resulting in the formation of calcium silicate hydrate phase(s). KEYWORDS Composite materials, glass fibres, tensile strength, environmental tests, tune-dependence, strength of materials, glass reinforced cement, fillers, pozzolanas, stresses, modulus of rupture, impact strength, weathering, stresses.
‘Department of the Environment, Bullding Research Establishment. Bullding Research Station, Garston, Watford. Crown CopyrIght
1980 -
Building Research Establishment
INTRODUCTION The use of inorganic fillers in concrete and other cement-based products is well known, for example silica flour in abestos cement. Some fillers are added as diluents for cement with a view to lowering the cost of the binder while others are incorporated in order to partake in chemical reactions with some of the cement hydration products notably calcium and hydroxyl ions. These latter fillers are known as pozzolanas of which pulverised fuel ash (pfa) is an important example. In general fillers reduce the initial strength of cement pastes even when they are pozzolanic. Other properties such as porosity and permeability are also modified. In glass fibre reinforced cement (grc) the use of sand as filler is essential in order to reduce the drying shrinkage to acceptable levels [I]. In the alkaline medium of hydrating cements sand will react with Cat+ and alkali metal ions in solution but only very slowly at normal ambient temperatures. Several silica containing fillers, some of them waste materials from various industries, also fall in this category. The effect of including some of
93
Properties
of grc containing
inorganic
fillers -.-I.
these materials in grc formulations on the long-term properties of the composite kept in different environments has been studied and the results are presented in this paper. For comparisons, the results obtained with grc containing a significant proportion of a typical pozzolana are also given. Some results obtained with other pozzolanas can be found elsewhere [2,3]. MATERIALS The inorganic fillers used in the present study were Fuller’s earth, china clay waste, quarry fines and an Italian pozzolana. Their chemical analyses are given in Table 1 together with some physical properties and mineralogical information. The waste sluge-bed material containing silica and clay minerals described as quarry fines was supplied in a wet lumpy state containing 80-80% water. Before addition to the cement slurry it was kept immersed in water for 24 hrs to break the lumps. The china clay waste was a mixture of coarse sand, micaceous residue, waste rock and clay which is left over
Table 1
Chemical, physical and mineralogical Fuller’s Earth
from the production of china clay. The Italian pozzolana was the Pozzolana Di Salone and Fuller’s earth was a high purity calcium montmorillonite clay. The glass fibres used in this study was Cem-FIL* alkali-resistant glass fibres. Each fibre strand consisted of 204 filaments of approximatety 13 pm diameter. COMPOSITE FA@RLCAATtohl AND CWatG The composite boards 4 m x 1 m and approximately 10 mm thick were produced by the mechanised BRE spray-suction method [4]. Appropriate amounts of the filler or pozzolana material were added to the cement and the mixture made into a slurry. Due to the very high specific surface area of Fuller’s earth a large amount of water was required for workability. In order to keep the final water/solid ratio (w/s) of the finished board similarto that of others, the proportion of this filler that could be incorporated in grc was about half of the other additions. Even then the w/s at 0.38 was much higher than in other boards (Table 2).
properties of inorganic fillers
Quarry Fines
China Clay Waste
Italian Pozzolana
97.45 0.85 0.03 0.02 0.05 -
44.51 16.26 9.70 4.03 0.80 10.29
(A) Chemical Analysis Oxides
T
% by weight 59.7 16.4 7.1 3.4 0.6 4.5 0.5 0.6 0.30 -
SiOz Al203 FezOX MgC TiOa CaO NazO KzO Mn304 SOS P*O5 Loss on ignition
70.79 10.78 4.80 1.71
0.65 2.08 0.87 2.96 0.12 -
0.02 0.25
1.70
5.73 0.20 0.003 -
6.90
0.23 4.19
0.01 0.29
6.60
2.38
2.73
2.66
2.66
5565
1425
3070
8240
Quartz, Feldspar, Mica, Clay
Quarts, Feldspar Zeolites, Pyroxenes
(B) Physical Properties Density (g/cm”) Surface area by Rigden cell
(cm’/g 1 (C) Mineralogical
phases present Montmorillonite Clay
*Trademark
94
of Fibreglass (UK) Ltd.
Quartz, Feldspar, Clay
Smgh and Majumda; _-_l_l___^__l--_
Properties of grc containing
Table 2
Composition
inorganic
Singh and Majumdar
fillers
of grc boards
1 Fillers
ltallan Pozzolana Chlna Clay Waste Fuller’s Earth Quarry Fines
% of fillers (by wt. of total solids)
% of glass fibre (by wt. 1
Final
40 40 20
5.17 4.83 4.87
0.28 0.30 0.38
40
5.45
0.28
The rnltlal curing of the composite boards followed the same procedure as used for standard grc and described previously [5]. Test specimens measuring 150 mm x 50 mm were kept in three different environments: air at 20 “C, 40% rh; water at 20 “C; and natural weathering on the exposure site at BRS. In addition, accelerated ageing of some of the specimens was carried out by keeping them under water at 60 “C for specified periods of time.
TESTING The properties measured were bending and tensile strength, Young’s modulus and impact strength. Limits of proportionality (LOP) in bending and tension and in some cases complete stress-strain diagrams were obtained using a Universal lnstron testing machine. The Impact strength was measured using an lzod tester of 12 J capacity. Usually six specimens were employed In all strength measurements and the average taken. The details of the test procedures employed in this study have been published [6]. The density of the composites was computed from the measured values of the weight and volume of 150 mm x 50 mm test coupons which were stored In air for 21 days following the initial 7 day wet curing. MICROSCOPY For obtaining mlcrostructural information some of the compostte samples stored for five years in the three different environments, a scanning electron microscope (SEM), was used. Both the fracture surfaces and ‘cleaved’ sections of the composite test specimens were examined. The SEM samples were mounted on alumlnlum stubs and coated with a layer of sputtered gold, 250X100 A thick. The operational procedures for examining composite specimens of the type used in this study have been described elsewhere 171. The matrix of aged grc samples was also examined, in some cases, by x-ray diffraction and differential thermai analvsis. RESULTS The modulus of rupture (MOR) and Limit of Proportional-
wls
ity (LOP) values of grc containing three different types of fillers and weathered on the exposure site at BRE for up to ten years are shown in figure 1. The corresponding impact strength data are shown in Figure 2. For comparison the average results obtained from a few grc boards made from OPC only are also included in Figures 1 and 2. The variation in the tensile strength of weathered grc containing 20% Fuller’s earth with time is compared with that observed for plain grc in Figure 3 and the stress-strain behaviour of the two materials after five years of natural weathering is illustrated in Figure 4. A summary of the properties of grc incorporating various types of fillers and kept in air and under water over long periods of time is given in Table 3. The MOR and impact strength values of grc incorporating three types of fillers and cured under hot water (60 “C) are shown in Figures 5 and 6. The fracture surfaces of grc containing 20% Fuller’s earth and kept in the three different environments for five years are illustrated in Figure 7 at low magnification. It is clearly seen that in continuous storage under water (Figure 7c), the material has a smooth fracture surface whereas for the other two environments, fracture faces have remained largely fibrous. The appearance of the fibre, the matrix and the f;bre/matrix interface in the weathered composite is seen in Figure 8 at high magnification. Some evidence of corrosion of the glass fibre is visible in Figure 8a and the growth of Ca(OH)* crystals in the space between the fibres is the most notable feature in Figure 8c. In Figure 9 the microstructure of a section of the fracture face of grc containing 40% Italian pozzolana after ten years of storage in water is shown. The fibre exhibits little sign of pitting or other imperfections and the interface is not as dense as in the case of standard grc. X-ray powder diffraction traces from the ten-yearaId grc specimens containing various fillers and kept under water showed that only in samples containing the Italian pozzolana there was firm evidence for the formation of a calcium-silicate hydrate (CSH) phase. In all cases the crystalline phases of the filler materials were found in the ten-year-old composite specimens together with CalOH h and the calcium aluminosulphate hydrates
95
Properties
of grc containing
inorganic
fillers -
Sngh and Majumchtr --l_-----_----.
-...-
40(a) “_(~~_____________~----------------
F
(c) (d)
l
10-
l
o-_--r-days
7
28
180
1 Age
Figure 1
- log
i
360
2
I
-LA.--
3
45
.i_
_i_.-J
8
IO
years
scale
MOR and LOP of grc containing (a)OPC (b)60% OPC 26% Fuller’s earth (c)60% OPC 40% quarry fines and (d) 60% OPC 40% china clay waste, subjected to natural weathering. Open symbols represent MOR and filled symbols LOP.
20-
5-
‘0
Oi._, days
1
I
7
28
780 Age
Figure 2
96
-log
i___;..
Liil
360 1
2
3
45
_.
8
L.-i
10
years
scale
Impact strength of grc containing (a) OPC (b)60% OPC 20% of Fuller's earth tc) 60% OPC 40% quarry fines and (d) 60% OPC 40% china clay waste; subjected to natural weathering.
Properties
of grc containing
inorganic
Singh and Majumdar
fillers
j-
I-
,
I
J
days
7
I
I
28
180
I
1 Age - log Figure3
Ultimatetensilestrengthofgrcmadefrom weathering.
(a)OPCand
I
I
2
3
I
I
360 45
years
scale (b)80%OPC20%
Fuller’searth;
subjected tonatural
w-----
I
I
0.2 Strain
0.3 -
0.4
%
I
Figure 4
Tensile stress-strain curves of grc made from (a) OPC, and (b) 80% OPC 20% Fuller’s earth; subjected to natural weathering for 5 years.
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) IS. IKJ/m*) p (g/cm”)
OPC (See references 8 and 9)
OPC 80% + Fuller’s Earth 20%
L_.__
.._
i 1.96
26
41 10 -
35 12 15 21
30 15 12 16
22
40 9 -
____
15
28 11
..___
17
16
23 1.87 36 15
32 IO
15 25
33 -
32 12 -
34 11 15 21
35-40 9-l 3 14-16 18-25
-
Air 40% RI-I -
1
Wate r
-. 34 12 5 12
19 15 9 9
19 13 8 6
26 11 11 12
22-25 16-19 9-l 2 8-l 0
l-
-
-
----
.._-. -
_____-
__-
7
20
9
4
6
-
-
I
-
5
11
-
-
Water
10 years
Air 40% RH
28 10 -.
17 15 -
4
7
17 16 -
15 14 -
-
3
12 -
19
-
Water
8 years
20 16 -
-.--.
--
--
23 13 8 6
21-25 16-19 9-l 2 4-6
30-35 IO-12 13-15 18-21
37 9 13 24
Water
-r
Air 40% Rt
5 years
Age and storage condition
Water
1 year
inorganic fillers
38 10 -
20 1 95 _.--.
---
--
39 8 17 28 1.90
35SO” 14-17* 14-17” 17-31* 2.02
Air 40% RH
I
T
different
28 days
containing
storage conditions
MOR (MN/m2) LOP (MN/m21 UTS (MN/m’i I.S. (KJ/m’! p b/cm”)
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) I.S. (KJlm’) p (g/cm”) -_
“. Total range for air and water
___.__,._. _.._.-. ~__.. .
OPC 60% Iitailan Pozzolana 40%
OPC 60% + China Clay Waste 40%
___._ __.-.___.--.
OPC 60% + Quarry Fines 40%
MOR (MN/m?) LOP (MN/m’) UTS (MN/m’) IS. (KJIm’) p (g/cm”)
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) I.S. (KJ/m*) p (g/cm”)
Property
Properties of grc composites
Matrix
Table 3
Properties
grc contaifling
of
4
inorganic
Singh and Majumdar
fillers
L-__-___
1
3
23
13
,
33
1
43
Age -days
L _______ MORofgrccompositescontaining (a)OPC(bf60%OPC40%quarryfines Figure5 (d)60%OPC 40% china clay waste; stored in water at 60 “C following
24 r-m
Figure6
(c)8O%OPC20% Fuller’searthand an initial 7 day cure.
1
lmpactstrengthofgrccompositescontaining (a)OPC(b)60%OPC40%quarryfines (c)80%OPCZO%Fuller’searth and (di 60% OPC 40% china clay waste; stored in water at 60 “C following an initial 7 day cure.
99
ProDerties of qrc containing
inorganic fillers
Singh and Majumdar
(a) notably ettringite. Differential thermal analysis results corroborated most of these findings, It must be pointed out thatthe detection and identification of the CSH phase by either x-ray or DTA methods is extremely difficult when small quantities of this phase are present in a mixture and the negative results reported here for three out of four fillers do not mean that CSH was not formed at all in some of these cases.
Figure 7
100
Fractured surface of 5yearold grccontaining ZO/Fuiler’s earth. (a) air stored, 40/ rh, 20 “C (blnatural weather (c)water stored 20 “C
DISCUSSION The results of the present study indicate (see Table 3) that for the relatively dry environment the long-term strength of grc in which a part of the cement has been replaced by Fuller’s earth or a pozzolanic material (such as the Italian variety investigated) will be similar to that of standard grc but the LOP and probably the stiffness also will be lower. These latter properties are matrix dependent and hence the dilution of cement affects them. The LOP values are substantially improved if the composite specimens are kept in water due to the larger extent of cement hydration. But the strength deteriorates since a greater degree of cement hydration promotes a stronger alkaline attack on the glass fibres. The results obtained with weathered materials show (Figures 1 and 2) that the incorporation of a non-pozzolanic filler in grc will perhaps always result in a reduction of the initial strength of the composite, but the long-term strength values may not be very different from those of standard grc. The failure strain of the composite at 5 years (Figure 4) is considerably higher in the case of grc containing 20% Fuller’s earth.
Properties
of grc containing
Srngh and Majumdar
morganic fillers
(bi
Accelerated ageing tests (Figures 5 and 6) showed that grc contarnrng drfferent types of fillers is likely to develop brittleness progressively In a manner similar to that encountered with ordtnary grc but Its long-term bending strengths can be higher if surtable filler materials are chosen; for instance china-clay waste and quarry fines have given encouraging results, Better results can perhaps be obtained through proper mix desigsn. The Italian pozzolana material when incorporated in grc as a filler has given long-term strengths in water storage that are superior to those of standard grc. This material reacts with cement hydration products readily producing CSH and the densrficatron of the interface caused primarily by the precipitation of CalOH )Zcrystals is less pronounced in this case (Figure 9). Consequently the impact strength of this composite IS superior to that of ordinary grc in the longer term 171. However its LOP values remain lower than that of standard grc throughout. It should be noted that the porzolana used had a very large specific surface area.
Figure 8
Fracture surface of 5 year old grc containing 20% Fuller’s earth after natural weathering. (a) surface attack on fibres (b) matrix showing abundance of Ca(OHL (c) growth of massive Ca(OHL crystals within fibre bundles
CONCLUSIONS 1. Non-pozzolanic inorganic ftllers when mixed In with cement to form the matrix of grc composites act mainly as a diluent and matrix controlled properties such as the limit of proportionality In bending are reduced. The inltral strength of the composrte is also reduced but the long-term strength is not affected much. By optimrsing the initial cure (e.g. under water at elevated temperatures) of the composite some fillers can probably give sufficiently high early strength to be of Interest In grc manufacture.
101
Properties
of grc containing
inorganic
Singh and Majumdar
fillers
carried out by Dr M. S. Stucke. The work described has been carried out as part of the research programme of the Building Research Establishment of the Department of the Environment and this paper is published by permission of the Director.
Figure 9
Microstructure of a section ofthe fracture face of grccontaining 40% Italian pozzalana afterten years of storage in water
2. Pozzolanic fillers such as the Italian pozzolana studied are useful in formulating mix designs for grc. In wet conditions grc containing the pozzolana has been found to have higher bending and impact strength in the long-term than those of standard grc but its LOP value remains lower. The beneficial effect of pozzolanas is due to the formation of CSH at the expense of crystalline Ca(OH12. This results in a relatively porous interface and perhaps the severity of the OH- ion attack on the glass fibre is also restricted.
ACKNOWLEDGEMENT Some of the microstructural
102
work
reported
here was
REFERENCES of drying 1 Lee, J. A. and West, T. R. ‘Measurement shrinkage of glass reinforced cement composites’, Proc RILEM Symp on Testing and Test Methods of Fibre Cement Composites, Sheffield, April 1978. Ed R. N. Swamy, The Construction Press Ltd, Lancaster, 1978, pp. 149-l 57. National Research Patent 1,402,555, 2. U.K. Development Corporation. U.K. Patent 1,565,823, Pilkington Brothers Limited. 3 Steele, B. R. ‘Prospects for fibre reinforced 4 construction materials’, Conf. Proc. of International Building Exhibition, London 1971, (Building Research Establishment, 1972 1, BRE CP 17/72. Ali, M. A., Majumdar, A. J. and Singh, B. ‘Properties 5 of glass fibre cement -the effect of fibre length and content’, J. Mater Sci., Vol. 10, 1975, pp. 1732-40. 6 Singh, B., Walton, P. L. and Stucke, M. S. ‘Testing and test methods of fibre cement composites’, Proc. RILEM Symp. on Testing and Test Methods of Fibre Cement Composites, Sheffield, April 1978, Ed. R. N. Swamy, The Construction Press Ltd., Lancaster, 1978, pp. 377-87. of 7 Stucke, M. S. and Majumdar, A. J. ‘Microstructure glass fibre reinforced cement composites’, J. Mater Sci., Vol. 11, 1976, pp. 1019-30. Building Research Establishment. A Study of the 8 Properties of Cem-FIL/OPC Composites. Current Paper 38/76. Garston, BRE 1976. Building Research Establishment. Properties of 9 GRC: ten year results. Information Paper IP 36/79. Garston, BRE 1979.
Journal of Cement Composites
and Lightweight
Properties of grc containing inorganic fillers 6.Singh and A. J. Majumdar”
Concrete,
Volume 3, Number 2
May 1981
SYNPOSIS Some of the strength properties of grc containing four different types of fillers have been determined for composites kept in three different environments up to IO years. These environments were relatively dry air and water both at 20 “C, and natural weathering conditions at Garston. The non-pozzolanic fillers such as china claywaste or quarry fines acted as diluents to the cement thereby lowering those properties of the composite such as the limit of proportionality that are matrix dependent. The long-term strength of grc is not affected in a major way by the addition of these fillers although the initial strength values are lower than those of standard grc. The Italian pozzolana used in the study has given encouraging results. The grc composites containing this filler has given 26 MN/m* as the modulus of rupture and 5 KJ/m’ as the impact strength after continuous storage under water for ten years, The corresponding values for standard grc are 17 MN/m* and 2 KJ/m’ respectively. It is believed that the improved properties of the modified grc is due to the chemical reaction between the pozzolana and Ca++ and OH- produced by the hydrating cement resulting in the formation of calcium silicate hydrate phase(s). KEYWORDS Composite materials, glass fibres, tensile strength, environmental tests, tune-dependence, strength of materials, glass reinforced cement, fillers, pozzolanas, stresses, modulus of rupture, impact strength, weathering, stresses.
‘Department of the Environment, Bullding Research Establishment. Bullding Research Station, Garston, Watford. Crown CopyrIght
1980 -
Building Research Establishment
INTRODUCTION The use of inorganic fillers in concrete and other cement-based products is well known, for example silica flour in abestos cement. Some fillers are added as diluents for cement with a view to lowering the cost of the binder while others are incorporated in order to partake in chemical reactions with some of the cement hydration products notably calcium and hydroxyl ions. These latter fillers are known as pozzolanas of which pulverised fuel ash (pfa) is an important example. In general fillers reduce the initial strength of cement pastes even when they are pozzolanic. Other properties such as porosity and permeability are also modified. In glass fibre reinforced cement (grc) the use of sand as filler is essential in order to reduce the drying shrinkage to acceptable levels [I]. In the alkaline medium of hydrating cements sand will react with Cat+ and alkali metal ions in solution but only very slowly at normal ambient temperatures. Several silica containing fillers, some of them waste materials from various industries, also fall in this category. The effect of including some of
93
Properties
of grc containing
inorganic
fillers -.-I.
these materials in grc formulations on the long-term properties of the composite kept in different environments has been studied and the results are presented in this paper. For comparisons, the results obtained with grc containing a significant proportion of a typical pozzolana are also given. Some results obtained with other pozzolanas can be found elsewhere [2,3]. MATERIALS The inorganic fillers used in the present study were Fuller’s earth, china clay waste, quarry fines and an Italian pozzolana. Their chemical analyses are given in Table 1 together with some physical properties and mineralogical information. The waste sluge-bed material containing silica and clay minerals described as quarry fines was supplied in a wet lumpy state containing 80-80% water. Before addition to the cement slurry it was kept immersed in water for 24 hrs to break the lumps. The china clay waste was a mixture of coarse sand, micaceous residue, waste rock and clay which is left over
Table 1
Chemical, physical and mineralogical Fuller’s Earth
from the production of china clay. The Italian pozzolana was the Pozzolana Di Salone and Fuller’s earth was a high purity calcium montmorillonite clay. The glass fibres used in this study was Cem-FIL* alkali-resistant glass fibres. Each fibre strand consisted of 204 filaments of approximatety 13 pm diameter. COMPOSITE FA@RLCAATtohl AND CWatG The composite boards 4 m x 1 m and approximately 10 mm thick were produced by the mechanised BRE spray-suction method [4]. Appropriate amounts of the filler or pozzolana material were added to the cement and the mixture made into a slurry. Due to the very high specific surface area of Fuller’s earth a large amount of water was required for workability. In order to keep the final water/solid ratio (w/s) of the finished board similarto that of others, the proportion of this filler that could be incorporated in grc was about half of the other additions. Even then the w/s at 0.38 was much higher than in other boards (Table 2).
properties of inorganic fillers
Quarry Fines
China Clay Waste
Italian Pozzolana
97.45 0.85 0.03 0.02 0.05 -
44.51 16.26 9.70 4.03 0.80 10.29
(A) Chemical Analysis Oxides
T
% by weight 59.7 16.4 7.1 3.4 0.6 4.5 0.5 0.6 0.30 -
SiOz Al203 FezOX MgC TiOa CaO NazO KzO Mn304 SOS P*O5 Loss on ignition
70.79 10.78 4.80 1.71
0.65 2.08 0.87 2.96 0.12 -
0.02 0.25
1.70
5.73 0.20 0.003 -
6.90
0.23 4.19
0.01 0.29
6.60
2.38
2.73
2.66
2.66
5565
1425
3070
8240
Quartz, Feldspar, Mica, Clay
Quarts, Feldspar Zeolites, Pyroxenes
(B) Physical Properties Density (g/cm”) Surface area by Rigden cell
(cm’/g 1 (C) Mineralogical
phases present Montmorillonite Clay
*Trademark
94
of Fibreglass (UK) Ltd.
Quartz, Feldspar, Clay
Smgh and Majumda; _-_l_l___^__l--_
Properties of grc containing
Table 2
Composition
inorganic
Singh and Majumdar
fillers
of grc boards
1 Fillers
ltallan Pozzolana Chlna Clay Waste Fuller’s Earth Quarry Fines
% of fillers (by wt. of total solids)
% of glass fibre (by wt. 1
Final
40 40 20
5.17 4.83 4.87
0.28 0.30 0.38
40
5.45
0.28
The rnltlal curing of the composite boards followed the same procedure as used for standard grc and described previously [5]. Test specimens measuring 150 mm x 50 mm were kept in three different environments: air at 20 “C, 40% rh; water at 20 “C; and natural weathering on the exposure site at BRS. In addition, accelerated ageing of some of the specimens was carried out by keeping them under water at 60 “C for specified periods of time.
TESTING The properties measured were bending and tensile strength, Young’s modulus and impact strength. Limits of proportionality (LOP) in bending and tension and in some cases complete stress-strain diagrams were obtained using a Universal lnstron testing machine. The Impact strength was measured using an lzod tester of 12 J capacity. Usually six specimens were employed In all strength measurements and the average taken. The details of the test procedures employed in this study have been published [6]. The density of the composites was computed from the measured values of the weight and volume of 150 mm x 50 mm test coupons which were stored In air for 21 days following the initial 7 day wet curing. MICROSCOPY For obtaining mlcrostructural information some of the compostte samples stored for five years in the three different environments, a scanning electron microscope (SEM), was used. Both the fracture surfaces and ‘cleaved’ sections of the composite test specimens were examined. The SEM samples were mounted on alumlnlum stubs and coated with a layer of sputtered gold, 250X100 A thick. The operational procedures for examining composite specimens of the type used in this study have been described elsewhere 171. The matrix of aged grc samples was also examined, in some cases, by x-ray diffraction and differential thermai analvsis. RESULTS The modulus of rupture (MOR) and Limit of Proportional-
wls
ity (LOP) values of grc containing three different types of fillers and weathered on the exposure site at BRE for up to ten years are shown in figure 1. The corresponding impact strength data are shown in Figure 2. For comparison the average results obtained from a few grc boards made from OPC only are also included in Figures 1 and 2. The variation in the tensile strength of weathered grc containing 20% Fuller’s earth with time is compared with that observed for plain grc in Figure 3 and the stress-strain behaviour of the two materials after five years of natural weathering is illustrated in Figure 4. A summary of the properties of grc incorporating various types of fillers and kept in air and under water over long periods of time is given in Table 3. The MOR and impact strength values of grc incorporating three types of fillers and cured under hot water (60 “C) are shown in Figures 5 and 6. The fracture surfaces of grc containing 20% Fuller’s earth and kept in the three different environments for five years are illustrated in Figure 7 at low magnification. It is clearly seen that in continuous storage under water (Figure 7c), the material has a smooth fracture surface whereas for the other two environments, fracture faces have remained largely fibrous. The appearance of the fibre, the matrix and the f;bre/matrix interface in the weathered composite is seen in Figure 8 at high magnification. Some evidence of corrosion of the glass fibre is visible in Figure 8a and the growth of Ca(OH)* crystals in the space between the fibres is the most notable feature in Figure 8c. In Figure 9 the microstructure of a section of the fracture face of grc containing 40% Italian pozzolana after ten years of storage in water is shown. The fibre exhibits little sign of pitting or other imperfections and the interface is not as dense as in the case of standard grc. X-ray powder diffraction traces from the ten-yearaId grc specimens containing various fillers and kept under water showed that only in samples containing the Italian pozzolana there was firm evidence for the formation of a calcium-silicate hydrate (CSH) phase. In all cases the crystalline phases of the filler materials were found in the ten-year-old composite specimens together with CalOH h and the calcium aluminosulphate hydrates
95
Properties
of grc containing
inorganic
fillers -
Sngh and Majumchtr --l_-----_----.
-...-
40(a) “_(~~_____________~----------------
F
(c) (d)
l
10-
l
o-_--r-days
7
28
180
1 Age
Figure 1
- log
i
360
2
I
-LA.--
3
45
.i_
_i_.-J
8
IO
years
scale
MOR and LOP of grc containing (a)OPC (b)60% OPC 26% Fuller’s earth (c)60% OPC 40% quarry fines and (d) 60% OPC 40% china clay waste, subjected to natural weathering. Open symbols represent MOR and filled symbols LOP.
20-
5-
‘0
Oi._, days
1
I
7
28
780 Age
Figure 2
96
-log
i___;..
Liil
360 1
2
3
45
_.
8
L.-i
10
years
scale
Impact strength of grc containing (a) OPC (b)60% OPC 20% of Fuller's earth tc) 60% OPC 40% quarry fines and (d) 60% OPC 40% china clay waste; subjected to natural weathering.
Properties
of grc containing
inorganic
Singh and Majumdar
fillers
j-
I-
,
I
J
days
7
I
I
28
180
I
1 Age - log Figure3
Ultimatetensilestrengthofgrcmadefrom weathering.
(a)OPCand
I
I
2
3
I
I
360 45
years
scale (b)80%OPC20%
Fuller’searth;
subjected tonatural
w-----
I
I
0.2 Strain
0.3 -
0.4
%
I
Figure 4
Tensile stress-strain curves of grc made from (a) OPC, and (b) 80% OPC 20% Fuller’s earth; subjected to natural weathering for 5 years.
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) IS. IKJ/m*) p (g/cm”)
OPC (See references 8 and 9)
OPC 80% + Fuller’s Earth 20%
L_.__
.._
i 1.96
26
41 10 -
35 12 15 21
30 15 12 16
22
40 9 -
____
15
28 11
..___
17
16
23 1.87 36 15
32 IO
15 25
33 -
32 12 -
34 11 15 21
35-40 9-l 3 14-16 18-25
-
Air 40% RI-I -
1
Wate r
-. 34 12 5 12
19 15 9 9
19 13 8 6
26 11 11 12
22-25 16-19 9-l 2 8-l 0
l-
-
-
----
.._-. -
_____-
__-
7
20
9
4
6
-
-
I
-
5
11
-
-
Water
10 years
Air 40% RH
28 10 -.
17 15 -
4
7
17 16 -
15 14 -
-
3
12 -
19
-
Water
8 years
20 16 -
-.--.
--
--
23 13 8 6
21-25 16-19 9-l 2 4-6
30-35 IO-12 13-15 18-21
37 9 13 24
Water
-r
Air 40% Rt
5 years
Age and storage condition
Water
1 year
inorganic fillers
38 10 -
20 1 95 _.--.
---
--
39 8 17 28 1.90
35SO” 14-17* 14-17” 17-31* 2.02
Air 40% RH
I
T
different
28 days
containing
storage conditions
MOR (MN/m2) LOP (MN/m21 UTS (MN/m’i I.S. (KJ/m’! p b/cm”)
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) I.S. (KJlm’) p (g/cm”) -_
“. Total range for air and water
___.__,._. _.._.-. ~__.. .
OPC 60% Iitailan Pozzolana 40%
OPC 60% + China Clay Waste 40%
___._ __.-.___.--.
OPC 60% + Quarry Fines 40%
MOR (MN/m?) LOP (MN/m’) UTS (MN/m’) IS. (KJIm’) p (g/cm”)
MOR (MN/m’) LOP (MN/m’) UTS (MN/m’) I.S. (KJ/m*) p (g/cm”)
Property
Properties of grc composites
Matrix
Table 3
Properties
grc contaifling
of
4
inorganic
Singh and Majumdar
fillers
L-__-___
1
3
23
13
,
33
1
43
Age -days
L _______ MORofgrccompositescontaining (a)OPC(bf60%OPC40%quarryfines Figure5 (d)60%OPC 40% china clay waste; stored in water at 60 “C following
24 r-m
Figure6
(c)8O%OPC20% Fuller’searthand an initial 7 day cure.
1
lmpactstrengthofgrccompositescontaining (a)OPC(b)60%OPC40%quarryfines (c)80%OPCZO%Fuller’searth and (di 60% OPC 40% china clay waste; stored in water at 60 “C following an initial 7 day cure.
99
ProDerties of qrc containing
inorganic fillers
Singh and Majumdar
(a) notably ettringite. Differential thermal analysis results corroborated most of these findings, It must be pointed out thatthe detection and identification of the CSH phase by either x-ray or DTA methods is extremely difficult when small quantities of this phase are present in a mixture and the negative results reported here for three out of four fillers do not mean that CSH was not formed at all in some of these cases.
Figure 7
100
Fractured surface of 5yearold grccontaining ZO/Fuiler’s earth. (a) air stored, 40/ rh, 20 “C (blnatural weather (c)water stored 20 “C
DISCUSSION The results of the present study indicate (see Table 3) that for the relatively dry environment the long-term strength of grc in which a part of the cement has been replaced by Fuller’s earth or a pozzolanic material (such as the Italian variety investigated) will be similar to that of standard grc but the LOP and probably the stiffness also will be lower. These latter properties are matrix dependent and hence the dilution of cement affects them. The LOP values are substantially improved if the composite specimens are kept in water due to the larger extent of cement hydration. But the strength deteriorates since a greater degree of cement hydration promotes a stronger alkaline attack on the glass fibres. The results obtained with weathered materials show (Figures 1 and 2) that the incorporation of a non-pozzolanic filler in grc will perhaps always result in a reduction of the initial strength of the composite, but the long-term strength values may not be very different from those of standard grc. The failure strain of the composite at 5 years (Figure 4) is considerably higher in the case of grc containing 20% Fuller’s earth.
Properties
of grc containing
Srngh and Majumdar
morganic fillers
(bi
Accelerated ageing tests (Figures 5 and 6) showed that grc contarnrng drfferent types of fillers is likely to develop brittleness progressively In a manner similar to that encountered with ordtnary grc but Its long-term bending strengths can be higher if surtable filler materials are chosen; for instance china-clay waste and quarry fines have given encouraging results, Better results can perhaps be obtained through proper mix desigsn. The Italian pozzolana material when incorporated in grc as a filler has given long-term strengths in water storage that are superior to those of standard grc. This material reacts with cement hydration products readily producing CSH and the densrficatron of the interface caused primarily by the precipitation of CalOH )Zcrystals is less pronounced in this case (Figure 9). Consequently the impact strength of this composite IS superior to that of ordinary grc in the longer term 171. However its LOP values remain lower than that of standard grc throughout. It should be noted that the porzolana used had a very large specific surface area.
Figure 8
Fracture surface of 5 year old grc containing 20% Fuller’s earth after natural weathering. (a) surface attack on fibres (b) matrix showing abundance of Ca(OHL (c) growth of massive Ca(OHL crystals within fibre bundles
CONCLUSIONS 1. Non-pozzolanic inorganic ftllers when mixed In with cement to form the matrix of grc composites act mainly as a diluent and matrix controlled properties such as the limit of proportionality In bending are reduced. The inltral strength of the composrte is also reduced but the long-term strength is not affected much. By optimrsing the initial cure (e.g. under water at elevated temperatures) of the composite some fillers can probably give sufficiently high early strength to be of Interest In grc manufacture.
101
Properties
of grc containing
inorganic
Singh and Majumdar
fillers
carried out by Dr M. S. Stucke. The work described has been carried out as part of the research programme of the Building Research Establishment of the Department of the Environment and this paper is published by permission of the Director.
Figure 9
Microstructure of a section ofthe fracture face of grccontaining 40% Italian pozzalana afterten years of storage in water
2. Pozzolanic fillers such as the Italian pozzolana studied are useful in formulating mix designs for grc. In wet conditions grc containing the pozzolana has been found to have higher bending and impact strength in the long-term than those of standard grc but its LOP value remains lower. The beneficial effect of pozzolanas is due to the formation of CSH at the expense of crystalline Ca(OH12. This results in a relatively porous interface and perhaps the severity of the OH- ion attack on the glass fibre is also restricted.
ACKNOWLEDGEMENT Some of the microstructural
102
work
reported
here was
REFERENCES of drying 1 Lee, J. A. and West, T. R. ‘Measurement shrinkage of glass reinforced cement composites’, Proc RILEM Symp on Testing and Test Methods of Fibre Cement Composites, Sheffield, April 1978. Ed R. N. Swamy, The Construction Press Ltd, Lancaster, 1978, pp. 149-l 57. National Research Patent 1,402,555, 2. U.K. Development Corporation. U.K. Patent 1,565,823, Pilkington Brothers Limited. 3 Steele, B. R. ‘Prospects for fibre reinforced 4 construction materials’, Conf. Proc. of International Building Exhibition, London 1971, (Building Research Establishment, 1972 1, BRE CP 17/72. Ali, M. A., Majumdar, A. J. and Singh, B. ‘Properties 5 of glass fibre cement -the effect of fibre length and content’, J. Mater Sci., Vol. 10, 1975, pp. 1732-40. 6 Singh, B., Walton, P. L. and Stucke, M. S. ‘Testing and test methods of fibre cement composites’, Proc. RILEM Symp. on Testing and Test Methods of Fibre Cement Composites, Sheffield, April 1978, Ed. R. N. Swamy, The Construction Press Ltd., Lancaster, 1978, pp. 377-87. of 7 Stucke, M. S. and Majumdar, A. J. ‘Microstructure glass fibre reinforced cement composites’, J. Mater Sci., Vol. 11, 1976, pp. 1019-30. Building Research Establishment. A Study of the 8 Properties of Cem-FIL/OPC Composites. Current Paper 38/76. Garston, BRE 1976. Building Research Establishment. Properties of 9 GRC: ten year results. Information Paper IP 36/79. Garston, BRE 1979.