The influence of polymer-modified mortar with fly ash was researched, when lignin cellulose and calcium sulphoaluminate expansive agent was added into mortar. The consistency, mechanical properties and shrinkage performance of mortar were studied by orthogonal experiment. Lignin cellulose was wrapped by the hydration products of binding materials. As the expansive agent and fly ash increasing, the consistency of mortar can be improved. Moreover, the influence of cement-based self-leveling material containing fly ash was also studied, when the different quantity of calcium oxide added into the material. The proper added quantity of CaO can largely improve the mechanical property and restrain the shrinkage of self-leveling material.
Trang 1Effects of lignin cellulose and expansive agent on microstructure and
macro-property of polymer-modified mortar containing fly ash
Quan Liuquana, Li Dongxua,*, Li Zongjinb
a
College of Material Science and Engineering, Nanjing University of Technology, Nanjing, Jiangsu 210009, China
b Department of Civil Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
a r t i c l e i n f o
Article history:
Received 14 July 2007
Received in revised form 3 July 2008
Accepted 4 July 2008
Available online 4 February 2009
Keywords:
Microstructure
Macro-property
Variance analysis
Lignin cellulose
Expansive agent
Polymer-modified mortar
a b s t r a c t
The influence of polymer-modified mortar with fly ash was researched, when lignin cellulose and calcium sulphoaluminate expansive agent was added into mortar The consistency, mechanical properties and shrinkage performance of mortar were studied by orthogonal experiment Lignin cellulose was wrapped
by the hydration products of binding materials As the expansive agent and fly ash increasing, the consistency of mortar can be improved Moreover, the influence of cement-based self-leveling material containing fly ash was also studied, when the different quantity of calcium oxide added into the material The proper added quantity of CaO can largely improve the mechanical property and restrain the shrink-age of self-leveling material
Ó 2009 Published by Elsevier Ltd
1 Introduction
Shrinkage of cement-based material is due to the loss of
capil-lary water in the process cement harden, main including dry
shrinkage due to water evaporation and spontaneous shrinkage
due to chemical shrinkage[1] When the shrinkage stress reaching
the some extent, cement-based material generate crack, so that the
mechanical property and durability would become bad When fiber
added into cement-based material, the amount of crack will be
sig-nificant reduced, meanwhile, the anti-crack, ductility and
durabil-ity of material will be significant improved[2,3] At present, there
are lots of researches about cement-based material with fibers,
these fibers including: nylon, polyethylene, polyamide fiber,
poly-ester fiber and so on[4,5]
Fly ash is the type of admixture material possessing potential
hydration activity Expansive agent is chemical material that can
react with cement and else gel, finally produce new substances
that can increase the volume of plaster[6,7] The research of lignin
cellulose added into polymer-modified mortar, especially the
re-search of polymer-modified mortar containing fly ash with both
lignin cellulose and expansive agent is few In view of this, the
per-formances of polymer-modified mortar with different quantity of
expansive agent, fly ash and lignin cellulose were studied in the
paper, moreover, the influences of cement-based self-leveling
material containing fly ash were researched, when added calcium
oxide Cement-based self-leveling material also belongs to poly-mer-modified mortar
2 Materials and methods 2.1 Raw materials Lignin cellulose (length is about 250lm); calcium oxide expansive agent and calcium sulphoaluminate expansive agent; methyl hydroxyethyl cellulose ether (H300P 2 ); redispersionable glue-powder (FL32); fly ash (the value of screen residue
is 0.4%, 0.08 mm); 52.5 grade Portland cement; fine sand and superfine sand; cal-cium lignosulfonate reducing agent; antifoamer The chemical composition of ce-ment and fly ash were showed Table 1
2.2 The orthogonal experiment of polymer-modified mortar The experiments were adopted by orthogonal design [8] Orthogonal ment is arranged many influence factors by orthogonal table Orthogonal experi-ment is a mathematics method that making use of principle of statistics to analyze results According to equalizing decentralization and neat comparability
of orthogonal experiment, researchers as long as do merely small amount experi-ments and are able to comprehensive discern both the condition of experiexperi-ments and the internal law of among factors There were three factors in the experiments, including expansive agent, lignin cellulose and fly ash In response to the require-ment of orthogonal experirequire-ment and the theory of polymer-modified mortar, the factors and levels were showed in Table 2 The added dosage of fly ash (20%, 35% and 50%) and calcium sulphoaluminate expansive agent (5%, 10% and 15%) were equivalent replaced cement The added dosage of lignin cellulose was 0.1%, 0.2% and 0.3% the dry weight of mortar According to the Chinese standard JGJ
98-2000 (Specification for mix proportion design of masonry mortar), in 1 m 3
mortar, the dosage of sand was 1443.7 kg/m 3 , the dosage of water was 300 kg/m 3 , the dos-age of cement was 265.1 kg/m 3 , moreover, the some dosage of methyl hydroxyethyl cellulose ether and calcium lignosulfonate were added into mortar Based on L9 0950-0618/$ - see front matter Ó 2009 Published by Elsevier Ltd.
* Corresponding author Tel.: +86 25 83587258; fax: +86 25 83588967.
E-mail address: dongxuli@njut.edu.cn (L Dongxu).
Contents lists available atScienceDirect Construction and Building Materials
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / c o n b u i l d m a t
Trang 2(3 3
), the experiment scheme was arranged, the programs of composition of mortar
were showed in Table 3 L9 (3 3
) means that the number of levels and factors were separate three, and the number of experiment group was nine.
2.3 The macro-property of polymer-modified mortar
The consistency of polymer-modified mortar was tested according to the
Chi-nese standard JGJ 70-90 (Standard for test method of basic properties of
construc-tion mortar) Three specimens of 40 mm 40 mm 160 mm size were prepared
for three-point flexure test After flexural test the specimens were cut from the
ends, i.e., from the uncracked portion of the specimens to obtain cubes of size
40 mm 40 mm 40 mm for determining compressive strength After moulding,
the specimens were allowed to cure in the mould for first 24 h The specimens were
then kept in the laboratory conditions, 20 ± 2 °C and 50 ± 5% relative humidity for
the next 27d It is known that the water curing has bad effect on mechanical
prop-erty of polymer-modified mortar [9]
The shrinkage crack reduction potential of lignin cellulose, fly ash and
expan-sive agent in mortar was evaluated For shrinkage tests of
25 mm 25 mm 280 mm size for each test were moulded After moulding, the
specimens were allowed to cure in the mould for first 24 h The specimens were
then kept in the curing conditions, 20 ± 1 °C and 95 ± 5% relative humidity The
shrinkage of mortars was studied by measuring the length of mortar specimens
at different curing age, by using electronic comparator.
The shrinkage ratios of cement mortar were calculated by formula, shown in the
following equation.
e¼Lt L0
Annotate
e– the shrinkage ratio of cement mortar (10 4 )
L 0 – the initial length of mortar specimens (mm)
L t – the length of mortar specimens every curing age (mm)
280 – the effective length of mortar specimens (mm)
2.4 The SEM of polymer-modified mortar
An approach of the microstructure can be made by means of image analysis For
this purpose, images were obtained in three steps: the preparation of plaster
spec-imens, the acquisition of images in the SEM, and the processing of images to obtain
preparation of mixes and of the drying process (2 days at 60 °C) In order to obtain the original interfacial structure of images, the polished treatment was not adopted After metallization, the sections were examined in a SEM, where the secondary electrons mode was used for imaging: compositions appear in white, and pores
in blank.
2.5 Effect of calcium oxide on the performance of self-leveling material Calcium oxide was added into self-leveling material by additive mix method.
Table 4 shows the mixing proportions of self-leveling material adding calcium oxide The flowability, shrinkage and 24 h strength of self-leveling material was tested by the Chinese standard JC/T985-2000 (cementitious self-leveling floor mortar).
3 Results and discussion 3.1 Consistency and mechanical property of polymer-modified mortar The results of experiments were analyzed by variance analysis Table 5shows the added dosage of expansive agent, lignin cellu-lose and fly ash can have some influence on the consistency of mortar The consistency of mortar can be improved by increasing the added dosage of expansive agent and fly ash But lignin cellu-lose has bad effect on the consistency of mortar The optimum mix proportion was M7 based on their consistency, from the re-sults of experiments The added dosage of fly ash and expansive agent were more, but the added dosage of lignin cellulose was less
in M7 than others The consistency of mortar can be improved by adding with fly ash The addition of fly ash can improve the fluidity
of cement paste, showing a water-reducing effect[10] The physi-cal and chemiphysi-cal characteristics of the fly ash, such as the grain morphology, volcanic glass structure, density, specific area, and grain diameter, have great influence on the water-reducing effect
of mortar There were lots of spherical grains (glass micro bead)
in fly ash But cement grains was irregular geometrically These glass micro beads play balls role in cement grains The resistance
of slippage of cement grains was reduced, so that the consistency
of mortar was increased The lignin cellulose was short rod struc-ture, the length was about 250lm When lignin cellulose mixed with plaster, they splice graft each other, so that lignin cellulose has bad effect on the consistency of mortar The testing of mortar consistency was finished in very short time, after added water into mixture Therefore, the physics structure of materials makes
great-Table 2
The factors level of orthogonal experiment L9(3 3
) wt.%
Table 3
L9(3 3
)The programs of composition and the testing results
Serial
number
Expansive
agent
wt.%
Lignin cellulose wt.%
Fly ash wt.%
Consistency (cm)
Flexural strength (MPa)
Compression strength (MPa)
Table 1
The chemical composition of cement and fly ash wt.%
CaO MgO Fe 2 O 3 Al 2 O 3 SiO 2 R 2 O SO 3 Loss
Cement 64.77 1.14 4.10 4.76 22.43 0.08 1.67 0.54
Fly ash 3.84 1.2 5.86 26.13 56.52 – 0.27 4.85
Table 4 The mixing proportions of self-leveling material with calcium oxide wt.% Serial
number Cement FL32 Superfine
sand
Fly ash H300P2 Calcium
oxide
Antifoamer
Table 5 Variance analysis of consistency
SS Degree of
freedom
Expansive agent 239.628 2 119.8142 2.05166 *
Lignin cellulose 625.360 2 312.6800 5.35423 *
*
Trang 3er influence on the consistency of mortar than the chemical
prop-erty of materials The fineness of expansive agent was very large
When mixed with other materials, expansive agent fills in both
ce-ment grains and fly ash grains The grain distribution of gel
mate-rial was meliorated, so that the consistency of mortar was
improved
Table 6shows expansive agent, lignin cellulose and fly ash have
some influence on the flexural strength of mortar.Table 7shows
according to the effects of composition on compression strength,
expansive agent was significance influence factor Fly ash was
rel-atively significance factor Both flexural strength and compression
strength of M7 were biggest in all programs of composition
Increasing the dosage of fly ash or expansive agent has bad effect
on the flexural strength and compression strength of mortar
Table 8shows when the interaction of both expansive agent and
fly ash being considered in variance analysis, both expansive agent
and fly ash played significance role on mechanical property of
mor-tar Moreover, the interaction of both expansive and fly ash was
relatively significance factor also There was alunite, gypsum and
so on in calcium sulphoaluminate expansive agent These chemical
substances can react with Ca(OH)2, producing AFm and AFt Fly ash
is pozzolanicity admixture and have potential activity, SiO2and
Al2O3can react with Ca(OH)2, produced hydraulicity gel The effect
of expansive agent and fly ash can exert, only when expansive agent and fly ash react with Ca(OH)2 In the experiments, the mor-tar specimens were made by adding fly ash and expansive agent, which equivalent replaced cement When the added dosage of fly ash and expansive agent to some degree, the quantity of Ca(OH)2
is not enough, expansive agent and fly ash effect would be not pref-erable exerted
3.2 Results of shrinkage of polymer-modified mortar The shrinkage ratios of polymer-modified mortar are showed in Table 9 The shrinkage ratios of mortar specimens were analyzed
by variance analysis The research results show that significance factors were alteration as the shrinkage of mortar specimens at dif-ferent curing age In response to the seventh day shrinkage ratios
of mortar s specimens, three influence factors (expansive agent, lignin cellulose, fly ash) were all not significance However, accord-ing to the 14th day shrinkage ratios of mortar specimens, three influence factors were all significance influence factor The phe-nomenon was largely related to the property of added materials [11]
Fly ash was the type of admixture material possessing potential hydration activity In the prior period of hydration, the hydration ability and surface energy of fly ash was low, the inter-particles water was easy evaporated, so that the dry shrinkage of mortar with fly ash was larger In the final period of hydration, fly ash take part in hydration with Ca(OH)2, which coming form the cement hydration[12] With the help of fly ash hydration, on the one hand, the carbonization shrinkage was reduced, on the other hand, the characteristics of mortar interface become dense, the loss of water was reduced and the dry shrinkage ratio of mortar were decreased [13] So that the ratio shrinkage of mortar containing fly ash was less than normal mortar’s in the final period
There was alunite, gypsum and so on in expansive agent These compositions can react with cement hydration product, producing possess of expansibility ettringite The expansive effect of expan-sive agent was largely related to the quantity of cement hydration products In the prior period of cement hydration, the quantity of cement hydration products was relatively few, So that the effect
of expansive agent was not exerted In the final period of cement hydration, the quantity of Ca(OH)2was few also, because Ca(OH)2 reacted with fly ash, the effect of expansive agent was weakened The phenomenon was certified by variance analysis of the 28th day shrinkage ratios, the expansive agent was not significance fac-tor at the curing age
According to 14th day shrinkage ratios of mortar specimens, lig-nin cellulose was significance factor Liglig-nin cellulose was wrapped
by the cement hydration products The shrinkage and expansion of mortar was controlled by the cohesive stress of between lignin cel-lulose and the hydrate of cement
Table 6
Variance analysis of flexural strength
SS Degree of
freedom
Expansive agent 1.70042 2 0.85021 8.55534 *
Lignin cellulose 0.18389 2 0.09194 0.92520 *
* Show relatively significance influence factor.
Table 7
Variance analysis of compressive strength
SS Degree of
freedom
Expansive agent 50.18002 2 25.09001 27.45044 **
Lignin cellulose 2.96949 2 1.48474 1.62443
Fly ash 32.28336 2 16.14168 17.66026 *
*
Show relatively significance influence factor.
** Show significance influence factor.
Table 8
Variance analysis of flexural strength when the interaction of both expansive agent
and fly ash was considered
SS Degree of
freedom
Expansive
agent
1.70042 2 0.85021 354.2546 **
Lignin
cellulose
Interaction 0.19635 1 0.19636 81.8148 *
* Show relatively significance influence factor.
**
Table 9 The shrinkage ratios of polymer-modified mortar (10 4 )
Trang 43.3 The SEM of polymer-modified mortar
Fig 1a shows that lignin cellulose (A) and aggregates (B) were
wrapped by the hydration products of binding material (C) The
bond of lignin cellulose and cement mortar matrix was better
There was a good agreement with the result ofFig 1b.Fig 1a also
shows that there were a lots of C–S–H gel on the surface of
aggre-gates There was appreciable variance the microstructure of both
pure cement mortar matrix and cement mortar matrix with fly
ash[14] There were lots of needle-volume hydration products in the pure cement mortar matrix The microstructure of pure cement mortar matrix was relatively loose The bond of needle-volume hydration products was little.Fig 1c shows that there were dense flocculent gel in cement mortar matrix with fly ash, and the bond
of the gel
3.4 Study of the property of cement-based self-leveling material The results of flowability and mechanical property were showedTable 10 When the added quantity of calcium oxide was below 1%, the flowability of the material was better than normal material’s However, the added quantity of calcium oxide was more than 1%, as the added quantity of calcium oxide increasing, the flowability of material become badly The added quantity of calcium oxide had not largely related to the material flowability loss, moreover, in some material mixing proportions, the 20 min’s flowability of materials were better than the initial flowability Table 10shows as the added quantity of calcium oxide increas-ing, even though the added quantity of calcium oxide was very low, the mechanical property of cement-based self-leveling material can be largely improved When the added quantity of calcium oxide was 1%, the flexural strength can improved 2.05 times than normal material, and the compression strength can improved 1.92 times After fly ash grinded, glass structure of fly ash was de-stroyed, active SiO2was exposed from glass structure and the sur-face area of fly ash was increased also This is due to grinded fly ash that exhibits pozzolanic properties and packing effect These char-acteristics tend to improve mortar strength as well as its density [15] The active SiO2can react with Ca(OH)2, produced hydraulicity gel[16] As a result that calcium oxide can produce lots of Ca(OH)2
in relatively short time, the self-leveling material added CaO can produce more hydraulicity gel than self-leveling material non-added CaO The early mechanical property of cement-based self-leveling material can be largely improved
Table 11shows as the added quantity of calcium oxide increas-ing, the shrinkage ratios of material were reduced When the added quantity of calcium oxide was 6%, the self-leveling material ap-pears slightly expanse When cement clinker react with water, the absolute volume of the system of cement–water is decreased,
Table 10 The testing results of flowability and mechanical of self-leveling material Serial
number
Flowability (cm)
20 min flowability (cm)
Flexural strength (MPa)
Compression strength (MPa)
Table 11 The ratios of shrinkage of self-leveling material (%)
Trang 5the phenomenon was said chemical shrinkage of material In the
hydration progress of cement, the shrinkage ratio of material
in-creased When calcium oxide added into cement-based
self-level-ing material, calcium oxide reacted with water, producself-level-ing
Ca(OH)2 In the progress, the volume of product increased 1.98
times than calcium oxide’s The hydration rate of calcium oxide
was quick, so that the expanse effect of calcium oxide has greater
influence than the chemical shrinkage of cement hydration in the
prior period of hydration The early shrinkage ratios of self-leveling
material containing calcium oxide appeared relatively small
4 Conclusions
1 As expansive agent and fly ash increasing, the consistency of
polymer-modified mortar can be improved Lignin cellulose
has bad effect on the consistency of polymer-modified mortar
2 When fly ash and calcium sulphoaluminate expansive agent
were added into mortar together, fly ash have not obvious effect
on the final strength of mortar, at the same time, the expanse
effect of expansive agent was also restricted This was not good
idea that both fly ash and calcium sulphoaluminate expansive
agent were added into mortar together
3 Lignin cellulose not only has advantage on the strength of
poly-mer-modified mortar, but also can effective control the
shrink-age property of polymer-modified mortar
4 The proper added quantity of CaO can largely improve the
mechanical property and restrain the shrinkage of material
Acknowledgments
The authors gratefully acknowledge the financial support for
this research from the National Basic Research Program of China
(2001CB610703) and a National Starch & Chemical Business
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