肖和
Ternary blending of cement with fly ash microsphere and condend silica fume to improve the performance of
mortar
Y.Li,A.K.H.Kwan ⇑
Department of Civil Engineering,The University of Hong Kong,Pokfulam,Hong Kong
a r t i c l e i n f o Article history:
Received 26May 2013
Received in revid form 26January 2014Accepted 20February 2014
起诉意见书
Available online 28February 2014Keywords:
Condend silica fume Fly ash microsphere Mortar
Packing density
Water film thickness
a b s t r a c t
The addition of condend silica fume (CSF)to fill into the voids between cement grains would relea the water entrapped there to form water films for lubrication.However,the large surface area of CSF would thin down the water film thickness (WFT).By adding also a cementitious material that is finer than cement but not as fine as CSF,such as fly ash microsphere (FAM),the water entrapped i
n the voids could be relead without excessively increasing the surface area.This may produce a larger WFT and better flowability than adding CSF alone.In this rearch,ternary blending of cement with FAM and CSF was studied by testing mortar mixes with different amounts of FAM and CSF added.It was found that the WFT is the key factor governing the properties of mortar and that ternary blending of cement with both FAM and CSF does offer some advantages.
Ó2014Elvier Ltd.All rights rerved.
1.Introduction
High-performance concrete (HPC),with high performance in both fresh and hardened states,is the future of our concrete indus-try [1].To produce HPC,it is esntial to lower the water/cementi-tious materials (W/CM)ratio;as suggested by Neville [2],‘‘what makes the concrete a high performance one is a very low water/ce-ment ratio’’.Such lowering of the W/CM ratio is made possible by the advent of superplasticizer (SP),which provides good workabil-ity even at very low W/CM ratio.However,since the water added must be more than sufficient to fill the voids in the bulk volume of the cementitious materials [3],there is a limit to which the W/CM ratio can be lowered,no matter how effective the SP is.This limit is not a constant,but is dependent on the packing density of the cementitious materials [4,5],which determines the volume of voids to be filled with water.
The addition of fine supplementary cementitious materials (SCM)to fill into the voids between cement grains is an effective way of increasing the packing density and reducing the volume of voids to be filled with water.With fine SCM particles filled into the voids,some of the water entrapped therein can be freed as ex-cess water (the water in excess of that needed to fill the voids)to form water films coating the solid particles to provide lubrication [6].This filling effect of fine SCM can produce a denr and more uniform mixture to improve the strength and durability of concrete [7].Moreover,the pozzolanic reaction of fine SCM can produce further gel products to improve the microstructure [8].In fact,concrete produced with fine SCMs added is often found to perform better in terms of workability,strength and durability [9–11].Various kinds of SCM,such as fly ash,ground granulated blast furnace slag,silica fume,metakaolin and rice husk ash,have emerged .Most of the SCMs are industrial by-products and their u can help to reduce the cement consumption and carbon foot-print of our concrete production [12–15].
The challenge in the application of SCM lies in the mix design.Due to the additional variable of SCM content,a much larger num-ber of trial batches are needed to arrive at the optimum mixture proportions [16].A scientific mix design method is desperately needed but is still lacking [17,18].Moreover,the effects of SCM on the fresh properties of concrete are not easy to predict beca
u of their dependence on the particle size distribution and shape of the SCM.For example,Kohno and Komatsu [19]reported that the addition of condend silica fume (CSF)would impair the flowabil-ity of mortar,while Duval and Kadri [20]demonstrated that the addition of CSF up to 10%by mass has no adver effect on the workability of concrete.More recently,Kwan and Fung [21]showed that the addition of CSF would increa the packing den-sity and thus improve the flowability of mortar.The contradic-tory results have made the mix design of HPC containing SCMs a difficult task.
Although the addition of fine SCM to fill into the voids between cement grains would no doubt increa the packing density and thus the amount of excess water available for forming water films,华为路由器密码
dx.doi/10.comp.2014.02.0020958-9465/Ó2014Elvier Ltd.All rights rerved.
⇑Corresponding author.Tel.:+852********;fax:+852********.
E-mail address:khkwan@hku.hk (A.K.H.Kwan).
it would at the same time increa the solid surface area to be coated with waterfilms[22].Ferraris et al.[23]suggested that the increas in packing density and solid surface area have oppo-site effects
on the rheology of cement paste.Whilst the increa in packing density would make available more excess water for form-ing waterfilms,the increa in solid surface area would thin down the thickness of waterfilms formed.Therefore,the net effect of addingfine SCM is dependent on the relative magnitudes of the in-crea in packing density and the increa in solid surface area.
To combine the two effects,Kwan and his rearch team advocated to u the waterfilm thickness(WFT),the average thick-ness of waterfilms coating the solid particles,as the controlling parameter in the mix design of HPC[24,25].They have also devel-oped a wet packing method for direct measurement of the packing density of solid particles in cement paste and mortar[26,27].From the packing density so measured,the excess water content may be calculated as the water content minus the voids volume and the WFT may be determined as the excess water to solid surface area ratio.The WFT has been found to be the single most important mix parameter governing the fresh properties of cement paste and mortar[24,28].
Being ultrafine,CSF is an effectivefiller for increasing the pack-ing density in order to relea more excess water to form water films.However,the large increa in solid surface area due to the highfineness of CSF would thin down the WFT.Hence,the addition of CSF may or may not increa the WFT.An intermediate sized SCM that isfiner than cement so as tofill into the voids between ceme
nt grains to increa the packing density but coarr than CSF so as to avoid large increa in the solid surface area may be more effective in increasing the WFT.Herein,it is propod that fly ash microsphere(FAM),which is a superfinefly ash captured from the exhaust smoke of coal-fired power stations,may be a suitable SCM for such usage.In fact,ternary blending of cement with both FAM and CSF may be even better becau successivefill-ing of the voids between cement grains byfirst the FAM particles and then the CSF particles should further increa the packing density.
Multiple blending of cement with more than one cementitious materials to harvest the synergic effect of the cementitious mate-rials is not new[29,30].In this regard,Aïtcin[31]has pointed out that there is a size gap between cement and CSF and that this size gap should be clod by adding an intermediate sized SCM. The authors concur with this statement and are proposing to ter-nary blend cement with both FAM and CSF so as to achieve a better particle size distribution.In this rearch,such ternary blending was studied by testing mortar mixes with different amounts of FAM,CSF and water added for their packing density,flowability, rheology,adhesiveness and strength.It will be en that the WFT remains a governing factor in the properties of such kind of mortar and that ternary blending with the size gap clod is superior to binary blending.
2.Materials
Three cementitious materials,namely,OPC(ordinary Portland cement),FAM and CSF,were employed in this study.The OPC was of strength class52.5N obtained locally in Hong Kong,whereas the FAM and CSF were imported from China and Europe,respec-tively.The OPC,FAM and CSF had been tested to comply with Euro-pean Standard EN197-1:2000[32],Chine Standard GB1596-91 [33]and American Standard ASTM C1240-03[34],respectively. Thefine aggregate ud was a crushed granite rockfine with a maximum size of1.18mm and a water absorption of1.02%by mass.The relative densities of the OPC,FAM,CSF andfine aggre-gate had been measured in accordance with the European Standards EN196-6:2010[35]or EN1097-6:2000[36]as3.11, 2.52,2.20and2.54,respectively.Their particle size distributions were measured by a lar diffraction particle size analyzer and the results obtained are plotted in Fig.1.Using the method pro-pod by Hunger and Brouwers[37],the specific surface areas of the OPC,FAM,CSF andfine aggregate were calculated from their particle size distributions as 1.12Â106, 3.95Â106,13.3Â106 and0.148Â106m2/m3,respectively.Unlike the cement grains, the FAM and CSF particles are spherical in shape.
The SP added was a polycarboxylate type supplied in the form of an aqueous solution with a solid mass content of20%and a rel-ative density of1.03.Since SP is a surface reactant and it is the SP dos
age per solid surface area that governs its effectiveness,the SP dosage was expresd in terms of the liquid mass of SP per solid surface area of the solid particles in mortar[38].Before tting the SP dosage to be ud,trial cement paste mixing with various SP dosages was carried out and it was found that for OPC alone, the saturation dosage of the SP(the dosage beyond which further addition yields little further increa inflowability)was 2.6Â10À5kg/m2.For simplicity,the SP dosage in terms of liquid mass of SP per solid surface area of the solid particles was t con-stant as2.6Â10À5kg/m2for all mortar samples.It should,how-ever,be noted that the saturation SP dosage could vary with the FAM and CSF contents,and this may have certain effects on the effectiveness of the SP added.
校园儿童画3.Experimental program
The experimental program consisted of three parts.Thefirst part was to measure the packing densities of the mortar samples having different FAM and CSF contents in order to study the effects of FAM and CSF on the packing density.The cond part was to measure theflow spread,flow rate,yield stress,apparent viscosity and adhesiveness of the mortar samples produced with different FAM,CSF and water contents.The last part was to measure the 28-day cube strength of the mortar samples.The WFT of each mor-tar sample was determined from the packing density results obtained in thefirst part and the W/CM ratio of the mortar.Then the testing results obtained in the cond and t
hird parts were cor-related to the WFT to study the roles of WFT in mortar with ternary blended cementitious materials.
In this study,the FAM and CSF contents were each expresd as a volumetric percentage of the total cementitious materials be-cau the packing density is governed by volume ratios rather than by mass ratios.Three FAM contents,namely,0%,20%and40%,and two CSF contents,namely,0%and10%,were adopted for the design of the mortar samples.The W/CM ratio was varied from0.4to
1.4
Y.Li,A.K.H.Kwan/Cement&Concrete Composites49(2014)26–3527
by volume while the cementitious materials tofine aggregate ratio wasfixed at0.75by volume.Table1depicts the detailed mix pro-portions of the mortar samples.In thefirst column,the mix num-bers were given in the format of M–X–Y–Z,where M denotes mortar,X and Y denote the FAM and CSF contents,respectively, and Z denotes the W/CM ratio by volume.The corresponding W/ CM ratios by mass were listed in the cond column of Table1 for reference.In total,42mortar samples were produced for testing.
Before making the mortar samples,thefine aggregate was con-ditioned in an environmental chamber until its moisture content, measured daily,has become constant.In the calculation of the amount of water to be added to the mortar sample,the water to be absorbed by thefine aggregate(water absorption minus moisture content)and the water content in the SP were taken into account.Each mortar sample was prepared using a standard mixer byfirst adding all the water to the mixer and then adding the solid ingredients and SP bit by bit into the mixer while mixing.This method has been found to be more effective than the conventional mixing method of adding all the water and solid ingredients to the mixer in one single batch,especially when the W/CM ratio is low and/or ultrafine materials such as CSF are added[26].All the mixing and testing procedures were carried out in a lab
oratory at
a temperature of24±2°C.
4.Test methods
4.1.Measurement of packing density
The packing densities of the mortar mixes containing OPC,FAM, CSF andfine aggregate were measured by a wet packing method developed by the authors’rearch team.This method was conducted under wet condition by mixing the solid particles with water and SP so that the effects of both water and SP could be incorporated.Details of the wet packing method have been pre-nted before[26].Basically,the wet packing method determines the packing density of the solid particles in a mortar as the maxi-mum solid concentration of the solid particles that can be achieved at different water/solid(W/S)ratios by volume.
4.2.Determination of WFT
Bad on the packing density result,the voids ratio of the particle system may be determined as:
Table1
Mix proportions,packing density and WFT.
Mix No.W/CM ratio by mass W/S ratio by volume Dosage of each ingredient in the mortar(kg/m3)Packing density(Voids ratio)WFT(l m)
OPC FAM CSF FA*Water SP
M-0-0-0.60.1930.2581061001146202120.735(0.361)À0.182 M-0-0-0.70.2250.301102600110822911À0.107 M-0-0-0.80.2570.34499300107325311À0.029 M-0-0-0.90.2890.387962001040276110.047 M-0-0-1.00.3210.430934001009298100.124 M-0-0-1.20.3860.51688100952338100.276 M-0-0-1.40.4500.6028340090137390.429
M-20-0-0.60.2000.25884917201146198170.768(0.302)À0.066 M-20-0-0.70.2340.3018211660110822516À0.001 M-20-0-0.80.2670.34479516101073250160.063 M-20-0-0.90.3010.38777015601040273150.128 M-20-0-1.00.3340.43074715101009295150.193 M-20-0-1.20.4010.5167051430952334140.322 M-20-0-1.40.4680.6026671350901370130.452
M-40-0-0.50.1740.21565935601187166220.797(0.255)À0.052 M-40-0-0.60.2090.25863734401146194220.004 M-40-0-0.70.2440.30161633201108221210.061 M-40-0-0.8
怎么切凤梨
0.2780.34459632201073246200.117 M-40-0-0.90.3130.38757731201040269200.173 M-40-0-1.00.3480.43056030201009291190.229 M-40-0-1.20.4170.5165282850952331180.342 M-40-0-1.40.4870.6025002700901367170.454
M-0-10-0.50.1660.2159890781187165230.800(0.250)À0.032 M-0-10-0.60.1990.2589550751146194220.007 M-0-10-0.80.2650.3448940701073245210.087 M-0-10-1.00.3310.4308400661009291200.166 M-0-10-1.20.3970.516793062952331180.246 M-0-10-1.40.4640.602750059901367170.325
M-20-10-0.40.1380.172797184801230130290.821(0.218)À0.035 M-20-10-0.50.1720.21576917878118716128À0.002 M-20-10-0.60.2070.258743172751146190270.030 M-20-10-0.80.2760.344695161701073241250.095 M-20-10-1.00.3450.430654151661009287240.160 M-20-10-1.20.4140.51661714362952327230.225 M-20-10-1.40.4820.60258413559901363210.290
M-40-10-0.40.1440.172569369801230126340.839(0.192)À0.013 M-40-10-0.50.1800.215549356781187157330.015 M-40-10-0.60.2160.258530344751146186320.042 M-40-10-0.80.2870.344497322701073238300.097 M-40-10-1.00.3590.430467302661009284280.152 M-40-10-1.20.4310.51644028562952324270.207 M-40-10-1.40.5030.60241727059901360250.261
*FA meansfine aggregate.
个人述职述廉报告28Y.Li,A.K.H.Kwan/Cement&Concrete Composites49(2014)26–35
u¼1À/max
/max
ð1Þ
军方反腐打虎榜where u is the voids ratio(the ratio of the volume of voids in the bulk volume to the solid volume of the solid particles)and/max is the maximum solid concentration of the solid particles.From the voids ratio so determined,the excess water ratio of the mortar can be evaluated as:
u0
w
¼u wÀuð2Þ
where u0
w
is the excess water ratio and u w is the water ratio(same as
the W/S ratio by volume)of the mortar.This excess water ratio has
the physical meaning of being the amount of excess water in the
mortar per solid volume of the particles.Meanwhile,the specific
surface area(defined as solid surface area per unit solid volume)
in the mortar A M can be calculated as:
A M¼A OPCÂR OPCþA FAMÂR FAMþA CSFÂR CSFþA FAÂR FAð3Þin which A OPC,A FAM,A CSF and A FA are respectively the specific surface areas of OPC,FAM,CSF andfine aggregate,whereas R OPC,R FAM,R CSF and R FA are respectively the volumetric ratios of OPC,FAM,CSF and
fine aggregate to the total solid volume.With the values of u0
w
and
A M so obtained,the WFT may be calculated as:
WFT¼u0
w
A M
ð4Þ
4.3.Measurement offlowability
Each mortar sample was subjected to the mini slump cone test and mini V-funnel test for evaluation of itsflowability in terms of flow spread andflow rate.Both the mini slump cone and mini V-funnel tests for mortar may be regarded as reduced scale versions of the slumpflow and V-funnel tests for concrete.There are veral versions of mini slump cone and mini V-funnel with different dimensions.The versions adopted here are the same as tho ud by Okamura and Ouchi[39].The detailed test procedures have been given before[24].
4.4.Measurement of rheological properties
Each mortar sample was subjected to the rheometer test for evaluation of its rheological properties in terms of yield stress and apparent viscosity.It was carried out using a speed-controlled rheometer equipped with a shear vane,measuring20mm in width and40mm in length,and a cylindrical container,having an inner diameter of40mm.The inner wall of the container was profiled with grooves of which the asperity was larger than the largest par-ticle in the mortar to minimize slippage during shearing.The de-tailed test procedures have been given before[24].
4.5.Measurement of adhesiveness
A new test,called stone rod adhesion test,recently developed by the author’s rearch team[40],was employed to measure the adhesiveness of the mortar samples.The apparatus consists of a handle with six stone rods verticallyfixed underneath and a container.The stone rods are made of granite,which is a com-monly ud rock for coar aggregate,and each stone rod has a diameter of10mm and an expod length of110mm.Before the test,the stone rods were immerd in water for at least24h and then wiped clean by a piece of dry cloth so that the stone rods were saturated and surface dry.During the test,the stone rods were im-merd into the mortar inside the container with a
n immersion depth of100mm,as indicated by the mortar surface reaching the100mm mark on the stone rods.The stone rods were left im-merd in the mortar for1min and afterwards pulled out steadily and slowly.The handle holding the stone rods was then placed on a stand to allow dripping to take place.After veral minutes when no more dripping occurred,the increa in weight of the handle (in other words,the weight of mortar adhering to the stone rods) was measured and taken as the adhesiveness of the mortar tested.
4.6.Measurement of strength
Three100mm cubes were made from each mortar sample for strength measurement.The cubes were made by placing the mortar into a cube mould,inrting a vibrator into the mortar for compaction and covering the top surface of the mould with a plas-tic sheet.After casting,the cubes were stored at a temperature of 24±2°C.After one day,the moulds were removed and the cubes were cured in a lime saturated water tank controlled at a temper-ature of27±2°C until the age of28days for cube compression test.
5.Experimental results
5.1.Packing density and voids ratio
The packing density and voids ratio results are tabulated in the tenth column of Table1.With only OPC and no FAM or CSF added, the mortar mix was measured to have a packing density of0.735. With OPC blended with FAM,the packing density was incread to 0.768at20%FAM content and to0.797at40%FAM content.With OPC blended with CSF,the packing density was incread to0.800 at10%CSF content.This demonstrates that the addition of either FAM or CSF can effectively improve the packing density of the solid particles in mortar.Relatively,the CSF is more effective becau it isfiner and canfill into the voids between cement grains more readily without looning the packing of the cement grains.
When the FAM and CSF were added together,the packing den-sity was further improved.With FAM already added,the addition of10%CSF incread the packing density to0.821at20%FAM con-tent and to0.839at40%FAM content.On the other hand,with10% CSF already added,the addition of20%and40%FAM incread the packing density to0.821and0.839,respectively.It may therefore be concluded that ternary blending with FAM and CSF is more effective than binary blending with either FAM or CSF in improving the packing density.This is due to successivefilling of the voids between the cement grains by the FAM and CSF particles.
By ternary blending with both FAM and CSF,the packing den-sity was incread from0.735to0.839by
14.1%,which atfirst sight does not appear to be large.However,the corresponding voids ratio was decread from0.361to0.192by46.8%,which is very large.Such decrea in voids ratio would substantially reduce the amount of water needed tofill the voids and increa the amount of excess water available for forming waterfilms.
5.2.Waterfilm thickness
The WFT results are listed in the last column of Table1and plotted against the W/S ratio for different FAM and CSF contents in Fig.2.All the WFT–W/S ratio curves are straight lines becau the WFT is a linear function of the W/S ratio.From thefigure,it can be en that some of mortar mixes have negative WFT values. When the WFT is negative,it no longer has the physical meaning as the average thickness of waterfilms coating the solid particles.A negative WFT value indicates that the amount of water in the mor-tar mix is not sufficient tofill the voids between the solid particles, leading to the entrapment of air in the unfilled voids and the formation of no waterfilms.
Y.Li,A.K.H.Kwan/Cement&Concrete Composites49(2014)26–3529
With only OPC and no FAM or CSF added,the WFT varied from À0.182l m at W/S ratio=0.26to0.429l m at W/S ratio=0.60. With20%FAM added,the WFT was incread toÀ0.066l m at W/S ratio=0.26an
d to0.452l m at W/S ratio=0.60.With40% FAM added,the WFT was further incread to0.004l m at W/S ratio=0.26and to0.454l m at W/S ratio=0.60.Hence,the addi-tion of FAM up to40%would significantly increa the WFT within the range of W/S covered in this study.The increa in WFT was generally larger at lower W/S ratio.This was becau of the propor-tionally larger increa in excess water at lower water content.On the other hand,with10%CSF but no FAM added,the WFT was in-cread to0.007l m at W/S ratio=0.26but decread to0.325l m at W/S ratio=0.60.The addition of CSF incread the WFT at W/S ratio60.45but decread the WFT at W/S ratio P0.50.Hence, the addition of CSF up to10%did not always increa the WFT.This was becau the CSF has a very large specific surface area and its addition has dramatically incread the solid surface area to be coated with waterfilms and thus thinned down the WFT,espe-cially at high W/S ratio when the proportional increa in excess water was relatively small.Lastly,with CSF already added,the addition of FAM up to40%incread the WFT at W/S ratio<0.40 but decread the WFT at W/S ratio>0.40.This was becau of the proportionally larger increa in excess water at lower W/S ratio and smaller increa in excess water at higher W/S ratio.
From the above,it is obvious that the FAM,which isfiner than OPC but not asfine as CSF,is effective in increasing the WFT over a wider range of W/S ratio than the CSF,while the CSF,which is the finest
of all,is more effective in increasing the WFT at very low W/S ratio.Hence,the optimum FAM and CSF contents for maximum WFT are dependent on the W/S ratio.In this ca,ternary blending of OPC with40%FAM and10%CSF is the optimum at W/S ratio <0.30but binary blending of OPC with40%FAM is the optimum
Table2
Flowability,rheological properties,adhesiveness and strength.
Mix No.Flow spread(mm)Flow rate(ml/s)Yield stress(Pa)Apparent viscosity(Pas)Adhesiveness(g)28-Day cube strength(MPa)
M-0-0-0.60.00.0––0.08.7
M-0-0-0.70.00.0––0.157.5
M-0-0-0.80.00.0––0.295.0
M-0-0-0.9 5.50.0–– 2.096.2
M-0-0-1.092.023.047.219.539.089.1
M-0-0-1.2182.0192.220.0 6.915.771.5
M-0-0-1.4210.0405.0 6.0 3.17.161.0
M-20-0-0.60.00.0––0.148.2
M-20-0-0.70.00.0––0.5116.2
M-20-0-0.857.50.0––23.4109.6
M-20-0-0.9111.567.532.014.048.2107.3
M-20-0-1.0151.0151.219.98.839.591.3
M-20-0-1.2210.0378.07.0 3.619.081.9
M-20-0-1.4225.0691.5 3.5 1.714.166.6
M-40-0-0.50.00.0––0.1117.3
M-40-0-0.60.00.0––0.8121.9
M-40-0-0.762.559.741.022.357.5109.0
M-40-0-0.8121.5143.520.411.143.3100.9
M-40-0-0.9153.5241.314.18.128.093.0
M-40-0-1.0191.0354.49.6 5.019.984.3
M-40-0-1.2238.5590.6 3.9 1.912.967.7
M-40-0-1.4247.5859.1 3.2 1.210.355.4
M-0-10-0.50.0–––0.098.6
M-0-10-0.60.0–––0.1117.6
M-0-10-0.889.049.623.721.339.6105.9
M-0-10-1.0172.0157.59.2 6.622.0102.2北京结婚落户
M-0-10-1.2243.0289.3 1.7 3.015.087.8
M-0-10-1.4269.0534.9 1.7 1.210.873.6
M-20-10-0.40.0–––0.0101.1
M-20-10-0.510.0––– 2.1118.5
M-20-10-0.661.017.238.723.456.9128.1
M-20-10-0.8157.5117.69.17.324.2105.3
M-20-10-1.0215.0234.3 4.3 4.117.285.3
M-20-10-1.2250.0363.5 3.2 2.88.783.5
M-20-10-1.4275.5578.6 1.60.78.667.5
M-40-10-0.47.0–––0.1119.8
M-40-10-0.557.5–53.432.159.7129.6
M-40-10-0.695.024.327.326.751.8117.4
M-40-10-0.8196.5140.3 4.9 6.618.695.9
M-40-10-1.0237.0265.0 2.7 4.010.088.1
M-40-10-1.2260.0457.3 1.9 1.4 5.770.2
M-40-10-1.4281.5603.2 1.60.7 5.253.4
30Y.Li,A.K.H.Kwan/Cement&Concrete Composites49(2014)26–35
