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Physico-mechanical properties of GAMMA induced polymer modified mortar
Radiat. Phys. Chem. Vol. 33, No. 6, pp. 533-537, 1989 Int. J. Radiat. Appl. Instrum., Part C Printed in Great Britain
0146-5724/89 $3.00+0.00 Pergamon Press plc
PHYSICO-MECHANICAL PROPERTIES OF GAMMA INDUCED POLYMER MODIFIED MORTAR M. R. ISMAIL National Centre for Radiation Research & Technology, Cairo, Egypt (Received 6 May 1988; in revised form 20 July 1988)
Abstract--The effect of a radiation initiated polymer on the physico-mechanical properties of polymer incorporated mortar has been investigated. The monomer used was methylmethacrylate with divinylbenzene as a crosslinking agent, used at concentrations ranging from 2 to 10% of methylmethacrylate and polymerization was carried out using ~-radiation from 5 to 25 kGy. The influence on polymer loading, compressive strength, water absorption, apparent porosity and bulk density, in addition to thermal behaviour (as investigated by DTA) of polymer incorporated in mortar, were studied. The results indicate that the polymer loading, compressive strength and bulk density increase with increases in percentage of divinylbenzene as well as with the y-radiation doses, whereas the water absorption and apparent porosity of the specimens decrease. This behaviour is attributed to the amount of polymer deposited in the pores of the samples.
INTRODUCTION
EXPERIMENTAL
Considerable research has shown that full polymer ipregnation of concrete specimens can lead to considerable improvements in virtually all the properties of concrete. In previous studies (Abo-El-Enein et al., 1981; EI-Miligy et al., 1981), polymer impregnated cement pastes using methylmethacrylate, styrene, acryionitrile showed an appreciable improvements in mechanical properties. The use of cross-linking monomers added in variable percentages to the basic monomers has been investigated (Rio and Bigini, 1975; Steinberg et aL, 1968, 1969). For a mixture of styrene 60% and TMPTMA 40% as well as a mixture of diallylphthalate 90% and methylmethacrylate 10%, the former gave the better results (Rio and Bigumi, 1975). Some investigators (Steinberg et al., 1968, 1969) found that the addition of TMPTMA to the monomers greatly reduced the radiation dose required to obtain 100% conversion. In addition, this monomer is capable of homopolymerizing by itself to form a completely three-dimensional cross-linked polymer. Also it can be incorporated in varying concentrations with other polymers to give crosslinked materials. Significant improvements in the structural and durability properties were obtained. The authors (Gebauer and Coughlin, 1971; Koos, 1974; Auskern et aL, 1972; Ramachandran and Sereda, 1973) investigated the possibility of the formation of organo-ealcium compounds in polymerimpregnated cements. The present study deals with the influence of methylmethacrylate and divinylbenzene mixtures and y-exposure dose on some physico-mechanical properties of polymer-modified mortar.
Materials
(1) A fresh commercial sample of ordinary (Type 1) Portland cement was used. Its chemical composition is as follows: CaO, 63.31; SiO2, 22.49; A1203, 5.2; Fe203, 2.92; MgO, 1.84; SO3, 2.07; free lime, 3.4; Insol. residue, 1.05 and ignition loss, 1.8%. The surface of the cement as measured by the Blainepermeability method is 2740 cm2/gm. (2) Sand. The sand used was obtained from Helwan district (near Cairo), has grain size between 0.18 and 0.25 mm and is almost free from organic or clay-like materials. (3) Organic monomers. (A) Methylmethacrylate (MMA) of BDH grade, stablized by hydroquinone. (B) Divinylbenzene (DVB) as crosslinking agent; it is stabalized with 4-terbutylphocatechol, produced by Riedel-de Harn, West Germany. Preparation o f the samples
Small cylindrical cement mortar test specimens, 25 mm dia. and 25 mm height, were prepared. These specimens, made from 1 : 3 cement: sand mixture and 10% water (of the total mix) were used for preparing the pastes. Demoulding was performed after 24 h, and then the samples were cured for 7 days in water at 24°C. Before impregnation, the specimens were dried at 105°C for 24 h and then subjected to physico-mechanical measurements and the results are as follows: compressive strength, 120kg/cm2; total porosity, 20; water absorption, 10% and bulk density, 1.962 g/cm 3. Impregnation was carried out as follows: The dried samples were evacuated at 10-2-10 -~ tort at room temperature for about 1 h
533
534
M.R. ISMAIL
and then soaked in the required monomer percentage for at least 3 h.
Radiation induced polymerization The impregnated specimens were wrapped in aluminium foil in order to minimize the loss of monomer from the pores of the samples by evaporation. Irradiation of the wrapped specimens was carried out by a [6°Co] source of the 7-Cell J. 6500 type, manufactured by the Atomic Energy of Canada (dose rate 10kGy/h). After radiation, the samples were dried at 50°C for 24h to remove excess monomer which did not polymerize. The mechanical compressive strength of the impregnated specimens was determined using an Instron type model, 1095, U.S.A. (max. weight 10 tons). The polymer loading ( % ) =
100(Wim
p -
WI)/WI,
where W~ of the weight of dried sample impregnation and W~0 is its weight after polymerization with 7-irradiation. The DTA runs were conducted using a Shimadzu type 30 thermal analyzer at a heating rate of 10c'C/min. RESULTS AND DISCUSSION
Polymer loading The effect of exposure dose of 7-irradiation on the polymer loading percentage of incorporated mortar shown in Fig. 1 indicates that the polymer loading percentage increases with an increase in percentage of DVB in the mixture. It also increases with the exposure dose for polymerization processes of the monomers. Utilization of such monomers allows simultaneous polymerization and the development of a cross-linked network; for example the compolymerization of a small amount of divinylbenzene with styrene yields a cross-linked polymer. Free radicals then continue formaton of their individual chains and indeed each chain may be formed at a different interval of time (Manson and Sperling, 1978). At low radiation intensities, a classical expression that has been experimentally confirmed for monomers states that the reaction rate is dependent
8
Compressive strength The variation of the compressive strength values as a function of polymer loading is given in Fig. 2. On the other hand, the variation of strength with exposure dose is shown in Fig. 3. The results of Fig. 2 indicate that the compressive strength increases for all samples impregnated with M M A alone or with a mixture of M M A and DVB over than those of the unimpregnated samples. The compressive strength at polymer loading 0.7% of P M M A (250 kg/cm 2) was more than double the strength of the unincorporated sample (12 kg/cm2). Also the strength increases up to 350 kg/cm 2 with increase of polymer loading of P M M A up to 3.8%. The strength also increases with the percentage of DVB in the monomer mixture, e.g. it reaches 550kg/cm 2 when 10% DVB was used. This occurs at a polymer loading of 7.5%. This 8
IO%DVB ~ - - - ~ ~_ . . . . ~ o 6 % OVB
/f-~
4
on the square root of the intensity (Chapiro, 1962; Charlesby, 1960). The rate of polymerization can therefore be increased by increasing the radiation intensity. At a high radiation intensity, or at high rates of radical inhibition, the polymerization rate reaches a value that does not increase further with increasing radiation intensity. These values can vary, depending on the monomer used and on the efficiency of radical production. According to the later discussion it is seen that, by using a DVB (multifunctional compound) as cross-linking agent with M M A for a radiation induced polymerization, the cross-linked network structure is enhanced, with increased DVB percentage. This result may be confirmed from the data of Fig. 1 which shows that the polymer loading percentage of the samples impregnated with M M A alone and polymerized in situ at 15 kGy is 2.7% but is 6.7% for the specimens impregnated with M M A + 10% DVB mixture and polymerized at the same dose of 7-radiation. On the other hand, the silicates which are found in the cement structure are effective for radiation in situ graft copolymerization of vinyl monomer system and cross-linking of their graft-copolymer (Theng, 1974).Therefore, the polymer loading percent of impregnated samples increases with the content of DVB in the mixture and it also increases due to the presence of silicates in the cement structure.
//9"
J
~-~o
f
4 % ova
~6
~ . . . ~ o MMA+zeto DVB
¢_
I
I
20 Exposure dose (kGy)
I
30
Fig. 1. Effects of exposure dose of ~-radiation on the polymer loading percentage of impregnated mortar.
+10% DVB
MMA+zero DVB
E ~2
t0
~
+4% DVB
6~oo
lo0
Compressive steng~h (kg cm-2)
Fig. 2. Effect of polymer loading percentage at various DVB concentrations and different doses (from 5-25 kGy) on the compressive strength of impregnated mortar.
500 == 400 ==
==
>= •~ 300 P
200
~ 1 10
v-Induced polymer modified mortar + 10% DVB oMMA+zero%DVB *MMA+4%
500
DVB
MMA÷ 1 0 % DVB
A + 4% OVB
400
,-E,,
ov. >= 300 E
8 1 20
Exposure
535
i 2
[ 30
dose (kGy)
Fig. 3. Variation of compressive strength of impregnated mortar as a function of DVB concentrations at various doses. increase is almost more than four times that of the control specimens. The mechanism by which the polymer strengthens the concrete is of great fundamental interest. One suggestion (Auskern and Horn, 1971) is that the polymer simply fills the void spaces of the concrete so that the strength of the composite begins to approach the idealized strength of pore-cement. Other investigators attribute the improved strength of various polymer impregnated building materials to such specific factors as enhanced interphase bonding and better resistance to crack growth. Hasselman and Penty (1973) have shown that impregnation with polymer of a substrate should result in a significant redistribution of stress concentrations between a pore and the matrix, even if the modulus of the polymer is low. According to the above mentioned, it can be concluded that the increase in strength in the present work is mainly dependent on the polymer content formed in the pores of the dried mortar specimens. This marked improvement in strength is probably attributed to one or more of the following: - - A n interaction between hydrated calcium silicates which are formed during the hydration reaction of cement mortar paste and the polymer formed in the pores during radiation-induced polymerization of monomers to form Si-C bond. As a result, the hydroxyl group present on the surface of the silicate materials is replaced by ethylenic radicals under the effect of ~,-irradiation. - - T h e amorphous hydrated cement constituents are recognized to increase the number of cross-links tO form a network structure, resulting in the eahancement of the mechanical strength of the samples. - - I t is also seen that, with increases in the amount of polymers further filling of pores and micro-cracks of the dried specimens probably occurs, so that the compressive strength of the composite approximately approaches that of the idealized pore-free
i 6
i 40
I 14
TotoL porosity (%)
Fig. 4. Relationship between total porosity and compressive strength of impregnated mortar at various DVB concentrations and exposure y-doses. cement paste. Figure 3 reflects the variation of the compressive strength with exposure dose for the impregnated samples having different percentage of DVB. Figure 4 shows the relation between compressive strength and total porosity; strength increases with decrease of total porosity. This holds for all the samples impregnated with M M A both in the absence or presence of DVB.
Bulk density Table (1) shows the influence of M M A either alone or with DVB at different concentrations, as well as exposure dose on the bulk density of incorporated specimens. The data of this table indicate that for a given 7 exposure dose, the bulk density increases with increasing DVB percentage. Furthermore for a given DVB concentration the bulk density of the impregnated samples increases with y-dose. This behaviour is attributed to the filling effect of the polymer in the porous system of the specimen. Due to the increase of radiation exposure dose and DVB percentage, the amount of polymer deposited in the pores is also increased, i.e. the amount of solid material is enhanced, leading to an increase of bulk density.
Total porosity Figure 5 illustrates the effect of various DVB percentages as well as exposure radiation dose on the Table 1. Bulk densityt of polymer incorporated samples of various divinylbenzen¢ percentage at different exposure dose
Exposure dose (kGy)
MMA+ %DVB
5
10
Zero 2% 4% 6% 8% 10%
2.015 2.084 2.095 2.103 2.111 2.119
2.053 2.093 2.101 2.114 2.116 2.126
15 2.071 2.069 2.117 2.128 2.120 ll41
20 2.081 2.104 2.122 2.136 2.129 2.168
25 2.096 2.117 2.130 2.140 2.158 2.188
tBulk density of the control sample = 1.962 g/cm 3.
536
M.R. ISMAIL DTA studies
o
8
MMA+zero DVB • 2 % OVB
6
2
+IO%DVB
I
i
I
10
20
30
E x p o s u r e dose
(kGy)
Fig. 5. Influence of polymer loading percentage on the total porosity of impregnated mortar at various exposures of v-doses for different DVB concentrations. total porosity of the impregnated samples. The results indicate that the apparent porosity decreases with increasing of dose and DVB percentage. This could be attributed to the filling effect of polymer deposited in the pores. The amount of polymer formed after 7-irradition polymerization is mainly dependent on the volume of pores and the amount of monomer introduced through the pores. The volume of the initial pores is approximately the same in samples prepared under the same conditions; therefore, the main factor which influences the total porosity of the specimen is the amount of monomer which polymerizes in these pores.
Figure 7 illustrates DTA thermograms of samples impregnated with either M M A or a mixture of M M A and various percentages of DVB irradiated to 20 kGy, together with the control sample. The effect of polymer is seen from the intensity of the endothermic effect at 480-520°C for Ca(OH)/ formed as result of hydration reaction of the mortar sample before impregnation. Also, the exothothermic effect at 380-400°C represents thermal degradation of the polymer present as a result polymerization. Figure 7 shows that almost all the polymercontaining samples reflect a low intensity of the endothermic peak of Ca(OH)2, compared with that of the control. The reduction increases with DVB percentage; the exothermic peak due to thermal degradation increases with DVB concentration. This effect is not seen by the control sample. Some investigators found that the characteristic endothermic peaks at 520°C for Ca(OH)2 was smaller as compared to neat cement paste, showing a remarkable decrease in quantity of Ca(OH)2 in polymercement due to a possible reaction between M M A and Ca(OH)2 (Gebauer and Coughlin, 1971). Further DTA studies (Ramachandran and Sereda, 1973) indicated the the thermal degradation of P M M A commenced before the Ca(OH)2 endotherm was reached
Water absorption Figure 6 shows the percentage of water absorption as a function of DVB and 7-dose. The results indicate that the water absorption of impregnated samples is continuously reduced with increasing polymer content. The water absorption is reduced to about 15% of its original values for 10% DVB in M M A at 15 kGy radiation. This leads to the conclusion that the polymerized product fills the porous system of the incorporated samples and decreases water absorption. Similar conclusions were obtained when using organic monomers--resulting in a reduction of water absorption values ranging between 83 and 93% (Steinberg et al., 1968, 1969).
T
.u_ E 0 P
UJ F-
o
E .c o c UJ
-~
+ zero DVB
2 i 5
I 10
~ ' ~ . . _ ~ ÷ 6 % DVB ~ " ~ + 8 % OvB I I ~'~ +IO%DVB 15 20 25
Exposure dose (kGy)
Fig. 6. Effects of various concentrations of DVB on water absorption percentage of impregnated mortar at different exposure v-irradiation dose.
100
~o6
3o0
400
Temperature (°C)
Fig. 7. DTA thermograms of impregnated mortar with various DVB cocentrations irradiated at 20 kGy.
~,-Induced polymer modified mortar at 520°C and that the decomposition products of PMMA reacted with Ca(OH)2. The results of Fig. 7 confirms this. On the other hand, the intensity of the exothermic peak at 380-400°C increases when increasing the percentage of DVB from 2-10% due to the deposition of higher amounts of polymer in the pores of the samples. It has to be mentioned that there is a small endotherm at about 103°C which has a definite tendency to increase with DVB concentration. This is associated with the Tg transition of PMMA (i.e. glassy to rubbery state) at Tg (at about 103°C). These conclusions are in good agreement with those of previous sections in the present work. REFERENCES
Abo-EI-Enein S. A., E1-Hemaly S. A. S., E1-MiligyA. A. and Zaidan M. R. (1981) Int. Congr. on Polymer Concrete, p. 782. Auskern A. and Horn W. (1971) J. Am. Ceram. Soc. 54, 282. Auskern A. and Horn W. (1973) The role of polymer in polymer impregnated concrete. BNL. 175-72.
RPC 33/6--E
537
Auskern A., Prachard T. and Horn W. (1972) BNL Rep., p. 16605. Chapiro A. (1962) Radiation Chemistry of Polymeric Systems. Interscience, New York. Charlesby A. (1960) Atomic Radiation and Polymers. Pergamon Press. Oxford. E1-Miligy A. A., Zaidan M. R., EI-Hemaly S. A. S. and Abo-E1-EenienS. A. (1981) Radiat. Phys. Chem. 17, 35. Gebauer J. and Coughlin R. W. (1971) Cem. Concrete Res. 1, 287. Gebauer J., Hasselman D. P. H. and Thomas D. A. (1972) J. Am. Ceram. Soc. 55, 175. Hasselman D. P. H. and Penty R. A. (1973) J. Am. Ceram. Soc. 56.
Koos J. (1974) 6th ICCC, Moscow. Manson J. A. and Sperling L. H. (1978) Polymer-Blends and Composites. U.S.A. Ramachandran V. S. and Sereda P. J. (1973) Thermo. Aeta 25, 433. Rio R. and BiginiS. (1975) Proc. First Int. Cong. on Polymer Concrete, May, 1975. Steinberg M. et al. (1968) Concrete-polymer material. First Topical Report, BNL. Steinberg M. et al. (1969) Concrete-polymer material. Second Topical Report, BNL. Theng B. K. G. (1974) The Chemistry o f the Clay Organic Reaction. Wiley, New York.
0146-5724/89 $3.00+0.00 Pergamon Press plc
PHYSICO-MECHANICAL PROPERTIES OF GAMMA INDUCED POLYMER MODIFIED MORTAR M. R. ISMAIL National Centre for Radiation Research & Technology, Cairo, Egypt (Received 6 May 1988; in revised form 20 July 1988)
Abstract--The effect of a radiation initiated polymer on the physico-mechanical properties of polymer incorporated mortar has been investigated. The monomer used was methylmethacrylate with divinylbenzene as a crosslinking agent, used at concentrations ranging from 2 to 10% of methylmethacrylate and polymerization was carried out using ~-radiation from 5 to 25 kGy. The influence on polymer loading, compressive strength, water absorption, apparent porosity and bulk density, in addition to thermal behaviour (as investigated by DTA) of polymer incorporated in mortar, were studied. The results indicate that the polymer loading, compressive strength and bulk density increase with increases in percentage of divinylbenzene as well as with the y-radiation doses, whereas the water absorption and apparent porosity of the specimens decrease. This behaviour is attributed to the amount of polymer deposited in the pores of the samples.
INTRODUCTION
EXPERIMENTAL
Considerable research has shown that full polymer ipregnation of concrete specimens can lead to considerable improvements in virtually all the properties of concrete. In previous studies (Abo-El-Enein et al., 1981; EI-Miligy et al., 1981), polymer impregnated cement pastes using methylmethacrylate, styrene, acryionitrile showed an appreciable improvements in mechanical properties. The use of cross-linking monomers added in variable percentages to the basic monomers has been investigated (Rio and Bigini, 1975; Steinberg et aL, 1968, 1969). For a mixture of styrene 60% and TMPTMA 40% as well as a mixture of diallylphthalate 90% and methylmethacrylate 10%, the former gave the better results (Rio and Bigumi, 1975). Some investigators (Steinberg et al., 1968, 1969) found that the addition of TMPTMA to the monomers greatly reduced the radiation dose required to obtain 100% conversion. In addition, this monomer is capable of homopolymerizing by itself to form a completely three-dimensional cross-linked polymer. Also it can be incorporated in varying concentrations with other polymers to give crosslinked materials. Significant improvements in the structural and durability properties were obtained. The authors (Gebauer and Coughlin, 1971; Koos, 1974; Auskern et aL, 1972; Ramachandran and Sereda, 1973) investigated the possibility of the formation of organo-ealcium compounds in polymerimpregnated cements. The present study deals with the influence of methylmethacrylate and divinylbenzene mixtures and y-exposure dose on some physico-mechanical properties of polymer-modified mortar.
Materials
(1) A fresh commercial sample of ordinary (Type 1) Portland cement was used. Its chemical composition is as follows: CaO, 63.31; SiO2, 22.49; A1203, 5.2; Fe203, 2.92; MgO, 1.84; SO3, 2.07; free lime, 3.4; Insol. residue, 1.05 and ignition loss, 1.8%. The surface of the cement as measured by the Blainepermeability method is 2740 cm2/gm. (2) Sand. The sand used was obtained from Helwan district (near Cairo), has grain size between 0.18 and 0.25 mm and is almost free from organic or clay-like materials. (3) Organic monomers. (A) Methylmethacrylate (MMA) of BDH grade, stablized by hydroquinone. (B) Divinylbenzene (DVB) as crosslinking agent; it is stabalized with 4-terbutylphocatechol, produced by Riedel-de Harn, West Germany. Preparation o f the samples
Small cylindrical cement mortar test specimens, 25 mm dia. and 25 mm height, were prepared. These specimens, made from 1 : 3 cement: sand mixture and 10% water (of the total mix) were used for preparing the pastes. Demoulding was performed after 24 h, and then the samples were cured for 7 days in water at 24°C. Before impregnation, the specimens were dried at 105°C for 24 h and then subjected to physico-mechanical measurements and the results are as follows: compressive strength, 120kg/cm2; total porosity, 20; water absorption, 10% and bulk density, 1.962 g/cm 3. Impregnation was carried out as follows: The dried samples were evacuated at 10-2-10 -~ tort at room temperature for about 1 h
533
534
M.R. ISMAIL
and then soaked in the required monomer percentage for at least 3 h.
Radiation induced polymerization The impregnated specimens were wrapped in aluminium foil in order to minimize the loss of monomer from the pores of the samples by evaporation. Irradiation of the wrapped specimens was carried out by a [6°Co] source of the 7-Cell J. 6500 type, manufactured by the Atomic Energy of Canada (dose rate 10kGy/h). After radiation, the samples were dried at 50°C for 24h to remove excess monomer which did not polymerize. The mechanical compressive strength of the impregnated specimens was determined using an Instron type model, 1095, U.S.A. (max. weight 10 tons). The polymer loading ( % ) =
100(Wim
p -
WI)/WI,
where W~ of the weight of dried sample impregnation and W~0 is its weight after polymerization with 7-irradiation. The DTA runs were conducted using a Shimadzu type 30 thermal analyzer at a heating rate of 10c'C/min. RESULTS AND DISCUSSION
Polymer loading The effect of exposure dose of 7-irradiation on the polymer loading percentage of incorporated mortar shown in Fig. 1 indicates that the polymer loading percentage increases with an increase in percentage of DVB in the mixture. It also increases with the exposure dose for polymerization processes of the monomers. Utilization of such monomers allows simultaneous polymerization and the development of a cross-linked network; for example the compolymerization of a small amount of divinylbenzene with styrene yields a cross-linked polymer. Free radicals then continue formaton of their individual chains and indeed each chain may be formed at a different interval of time (Manson and Sperling, 1978). At low radiation intensities, a classical expression that has been experimentally confirmed for monomers states that the reaction rate is dependent
8
Compressive strength The variation of the compressive strength values as a function of polymer loading is given in Fig. 2. On the other hand, the variation of strength with exposure dose is shown in Fig. 3. The results of Fig. 2 indicate that the compressive strength increases for all samples impregnated with M M A alone or with a mixture of M M A and DVB over than those of the unimpregnated samples. The compressive strength at polymer loading 0.7% of P M M A (250 kg/cm 2) was more than double the strength of the unincorporated sample (12 kg/cm2). Also the strength increases up to 350 kg/cm 2 with increase of polymer loading of P M M A up to 3.8%. The strength also increases with the percentage of DVB in the monomer mixture, e.g. it reaches 550kg/cm 2 when 10% DVB was used. This occurs at a polymer loading of 7.5%. This 8
IO%DVB ~ - - - ~ ~_ . . . . ~ o 6 % OVB
/f-~
4
on the square root of the intensity (Chapiro, 1962; Charlesby, 1960). The rate of polymerization can therefore be increased by increasing the radiation intensity. At a high radiation intensity, or at high rates of radical inhibition, the polymerization rate reaches a value that does not increase further with increasing radiation intensity. These values can vary, depending on the monomer used and on the efficiency of radical production. According to the later discussion it is seen that, by using a DVB (multifunctional compound) as cross-linking agent with M M A for a radiation induced polymerization, the cross-linked network structure is enhanced, with increased DVB percentage. This result may be confirmed from the data of Fig. 1 which shows that the polymer loading percentage of the samples impregnated with M M A alone and polymerized in situ at 15 kGy is 2.7% but is 6.7% for the specimens impregnated with M M A + 10% DVB mixture and polymerized at the same dose of 7-radiation. On the other hand, the silicates which are found in the cement structure are effective for radiation in situ graft copolymerization of vinyl monomer system and cross-linking of their graft-copolymer (Theng, 1974).Therefore, the polymer loading percent of impregnated samples increases with the content of DVB in the mixture and it also increases due to the presence of silicates in the cement structure.
//9"
J
~-~o
f
4 % ova
~6
~ . . . ~ o MMA+zeto DVB
¢_
I
I
20 Exposure dose (kGy)
I
30
Fig. 1. Effects of exposure dose of ~-radiation on the polymer loading percentage of impregnated mortar.
+10% DVB
MMA+zero DVB
E ~2
t0
~
+4% DVB
6~oo
lo0
Compressive steng~h (kg cm-2)
Fig. 2. Effect of polymer loading percentage at various DVB concentrations and different doses (from 5-25 kGy) on the compressive strength of impregnated mortar.
500 == 400 ==
==
>= •~ 300 P
200
~ 1 10
v-Induced polymer modified mortar + 10% DVB oMMA+zero%DVB *MMA+4%
500
DVB
MMA÷ 1 0 % DVB
A + 4% OVB
400
,-E,,
ov. >= 300 E
8 1 20
Exposure
535
i 2
[ 30
dose (kGy)
Fig. 3. Variation of compressive strength of impregnated mortar as a function of DVB concentrations at various doses. increase is almost more than four times that of the control specimens. The mechanism by which the polymer strengthens the concrete is of great fundamental interest. One suggestion (Auskern and Horn, 1971) is that the polymer simply fills the void spaces of the concrete so that the strength of the composite begins to approach the idealized strength of pore-cement. Other investigators attribute the improved strength of various polymer impregnated building materials to such specific factors as enhanced interphase bonding and better resistance to crack growth. Hasselman and Penty (1973) have shown that impregnation with polymer of a substrate should result in a significant redistribution of stress concentrations between a pore and the matrix, even if the modulus of the polymer is low. According to the above mentioned, it can be concluded that the increase in strength in the present work is mainly dependent on the polymer content formed in the pores of the dried mortar specimens. This marked improvement in strength is probably attributed to one or more of the following: - - A n interaction between hydrated calcium silicates which are formed during the hydration reaction of cement mortar paste and the polymer formed in the pores during radiation-induced polymerization of monomers to form Si-C bond. As a result, the hydroxyl group present on the surface of the silicate materials is replaced by ethylenic radicals under the effect of ~,-irradiation. - - T h e amorphous hydrated cement constituents are recognized to increase the number of cross-links tO form a network structure, resulting in the eahancement of the mechanical strength of the samples. - - I t is also seen that, with increases in the amount of polymers further filling of pores and micro-cracks of the dried specimens probably occurs, so that the compressive strength of the composite approximately approaches that of the idealized pore-free
i 6
i 40
I 14
TotoL porosity (%)
Fig. 4. Relationship between total porosity and compressive strength of impregnated mortar at various DVB concentrations and exposure y-doses. cement paste. Figure 3 reflects the variation of the compressive strength with exposure dose for the impregnated samples having different percentage of DVB. Figure 4 shows the relation between compressive strength and total porosity; strength increases with decrease of total porosity. This holds for all the samples impregnated with M M A both in the absence or presence of DVB.
Bulk density Table (1) shows the influence of M M A either alone or with DVB at different concentrations, as well as exposure dose on the bulk density of incorporated specimens. The data of this table indicate that for a given 7 exposure dose, the bulk density increases with increasing DVB percentage. Furthermore for a given DVB concentration the bulk density of the impregnated samples increases with y-dose. This behaviour is attributed to the filling effect of the polymer in the porous system of the specimen. Due to the increase of radiation exposure dose and DVB percentage, the amount of polymer deposited in the pores is also increased, i.e. the amount of solid material is enhanced, leading to an increase of bulk density.
Total porosity Figure 5 illustrates the effect of various DVB percentages as well as exposure radiation dose on the Table 1. Bulk densityt of polymer incorporated samples of various divinylbenzen¢ percentage at different exposure dose
Exposure dose (kGy)
MMA+ %DVB
5
10
Zero 2% 4% 6% 8% 10%
2.015 2.084 2.095 2.103 2.111 2.119
2.053 2.093 2.101 2.114 2.116 2.126
15 2.071 2.069 2.117 2.128 2.120 ll41
20 2.081 2.104 2.122 2.136 2.129 2.168
25 2.096 2.117 2.130 2.140 2.158 2.188
tBulk density of the control sample = 1.962 g/cm 3.
536
M.R. ISMAIL DTA studies
o
8
MMA+zero DVB • 2 % OVB
6
2
+IO%DVB
I
i
I
10
20
30
E x p o s u r e dose
(kGy)
Fig. 5. Influence of polymer loading percentage on the total porosity of impregnated mortar at various exposures of v-doses for different DVB concentrations. total porosity of the impregnated samples. The results indicate that the apparent porosity decreases with increasing of dose and DVB percentage. This could be attributed to the filling effect of polymer deposited in the pores. The amount of polymer formed after 7-irradition polymerization is mainly dependent on the volume of pores and the amount of monomer introduced through the pores. The volume of the initial pores is approximately the same in samples prepared under the same conditions; therefore, the main factor which influences the total porosity of the specimen is the amount of monomer which polymerizes in these pores.
Figure 7 illustrates DTA thermograms of samples impregnated with either M M A or a mixture of M M A and various percentages of DVB irradiated to 20 kGy, together with the control sample. The effect of polymer is seen from the intensity of the endothermic effect at 480-520°C for Ca(OH)/ formed as result of hydration reaction of the mortar sample before impregnation. Also, the exothothermic effect at 380-400°C represents thermal degradation of the polymer present as a result polymerization. Figure 7 shows that almost all the polymercontaining samples reflect a low intensity of the endothermic peak of Ca(OH)2, compared with that of the control. The reduction increases with DVB percentage; the exothermic peak due to thermal degradation increases with DVB concentration. This effect is not seen by the control sample. Some investigators found that the characteristic endothermic peaks at 520°C for Ca(OH)2 was smaller as compared to neat cement paste, showing a remarkable decrease in quantity of Ca(OH)2 in polymercement due to a possible reaction between M M A and Ca(OH)2 (Gebauer and Coughlin, 1971). Further DTA studies (Ramachandran and Sereda, 1973) indicated the the thermal degradation of P M M A commenced before the Ca(OH)2 endotherm was reached
Water absorption Figure 6 shows the percentage of water absorption as a function of DVB and 7-dose. The results indicate that the water absorption of impregnated samples is continuously reduced with increasing polymer content. The water absorption is reduced to about 15% of its original values for 10% DVB in M M A at 15 kGy radiation. This leads to the conclusion that the polymerized product fills the porous system of the incorporated samples and decreases water absorption. Similar conclusions were obtained when using organic monomers--resulting in a reduction of water absorption values ranging between 83 and 93% (Steinberg et al., 1968, 1969).
T
.u_ E 0 P
UJ F-
o
E .c o c UJ
-~
+ zero DVB
2 i 5
I 10
~ ' ~ . . _ ~ ÷ 6 % DVB ~ " ~ + 8 % OvB I I ~'~ +IO%DVB 15 20 25
Exposure dose (kGy)
Fig. 6. Effects of various concentrations of DVB on water absorption percentage of impregnated mortar at different exposure v-irradiation dose.
100
~o6
3o0
400
Temperature (°C)
Fig. 7. DTA thermograms of impregnated mortar with various DVB cocentrations irradiated at 20 kGy.
~,-Induced polymer modified mortar at 520°C and that the decomposition products of PMMA reacted with Ca(OH)2. The results of Fig. 7 confirms this. On the other hand, the intensity of the exothermic peak at 380-400°C increases when increasing the percentage of DVB from 2-10% due to the deposition of higher amounts of polymer in the pores of the samples. It has to be mentioned that there is a small endotherm at about 103°C which has a definite tendency to increase with DVB concentration. This is associated with the Tg transition of PMMA (i.e. glassy to rubbery state) at Tg (at about 103°C). These conclusions are in good agreement with those of previous sections in the present work. REFERENCES
Abo-EI-Enein S. A., E1-Hemaly S. A. S., E1-MiligyA. A. and Zaidan M. R. (1981) Int. Congr. on Polymer Concrete, p. 782. Auskern A. and Horn W. (1971) J. Am. Ceram. Soc. 54, 282. Auskern A. and Horn W. (1973) The role of polymer in polymer impregnated concrete. BNL. 175-72.
RPC 33/6--E
537
Auskern A., Prachard T. and Horn W. (1972) BNL Rep., p. 16605. Chapiro A. (1962) Radiation Chemistry of Polymeric Systems. Interscience, New York. Charlesby A. (1960) Atomic Radiation and Polymers. Pergamon Press. Oxford. E1-Miligy A. A., Zaidan M. R., EI-Hemaly S. A. S. and Abo-E1-EenienS. A. (1981) Radiat. Phys. Chem. 17, 35. Gebauer J. and Coughlin R. W. (1971) Cem. Concrete Res. 1, 287. Gebauer J., Hasselman D. P. H. and Thomas D. A. (1972) J. Am. Ceram. Soc. 55, 175. Hasselman D. P. H. and Penty R. A. (1973) J. Am. Ceram. Soc. 56.
Koos J. (1974) 6th ICCC, Moscow. Manson J. A. and Sperling L. H. (1978) Polymer-Blends and Composites. U.S.A. Ramachandran V. S. and Sereda P. J. (1973) Thermo. Aeta 25, 433. Rio R. and BiginiS. (1975) Proc. First Int. Cong. on Polymer Concrete, May, 1975. Steinberg M. et al. (1968) Concrete-polymer material. First Topical Report, BNL. Steinberg M. et al. (1969) Concrete-polymer material. Second Topical Report, BNL. Theng B. K. G. (1974) The Chemistry o f the Clay Organic Reaction. Wiley, New York.