Viscosity and water demand of limestone- and fly ash-blended cement pastes in the presence of superplasticisers

Construction and Building Materials 48 (2013) 417–423

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Viscosity and water demand of limestone- and fly ash-blended cement pastes in the presence of superplasticisers O. Burgos-Montes, M.M. Alonso, F. Puertas ⇑ Eduardo Torroja Institute for Construction Science (IETcc-CSIC), Madrid, Spain

h i g h l i g h t s  Krieger–Dougherty equation could predict the viscosity of blended cement suspensions.  The use of mineral additions reduced the effectiveness of cement superplasticizers.  Cement with limestone under 30% had little effect on paste rheology.  Fly ash lowers the minimum water demand for suitable fluidity.

a r t i c l e

i n f o

Article history: Received 19 March 2013 Received in revised form 18 June 2013 Accepted 9 July 2013

Keywords: Viscosity w/c Ratio Cement pastes Limestone Fly ash Rheology Superplasticisers

a b s t r a c t The rheological behaviour of fresh cement has a direct effect on the microstructural development of mortar and concrete. Inasmuch as the presence of mineral additions impact cement paste rheology and consequently its permanent microstructure and strength, a full understanding of blended cement behaviour should be pursued. The present study addresses the joint effect of mineral additions (limestone and fly ash) and superplasticisers admixtures on the viscosity and water demand of cement pastes. Cement pastes were prepared with 10, 30 or 50 wt% limestone or fly ash as mineral admixtures. Melamine-, naphthalene- and polycarboxylate-based superplasticisers were used. Paste rheology was studied in terms of variations in yield stress and viscosity with the solids content and amount of mineral additions added. The strength and microstructure of the blended cement pastes were determined at viscosity values of 1.5 Pas. in the presence of superplasticisers. The findings showed that the Krieger–Dougherty equation could be used to determine the effect of solids content on the apparent viscosity of limestone- and fly ash-blended cement suspensions, as well as the effect of superplasticisers. Adding less than 30% limestone to cement had no effect on paste rheology: i.e., the w/c ratios for minimum and optimal workability were similar to the ratios for ordinary cement. However, adding fly ash did lower the minimum water demand, and the optimal amount of water needed for suitable fluidity. The inclusion of 10% of either addition raised paste strength, while higher proportions 30 or 50%) had the opposite effect. The use of mineral additions reduced the effectiveness of cement superplasticisers. Ó 2013 Published by Elsevier Ltd.

1. Introduction One of the key factors in the development of concrete microstructure is its fresh state fluidity. Workability is the term traditionally used to define a concrete that can be readily mixed, shipped and placed. Workability is typically determined by means of the slump test, although different concrete mixes with similar slump values have been reported to behave differently during on-site casting. Given the essential role in concrete fluidity played by fresh cement rheology, a detailed study is needed to define the

⇑ Corresponding author. E-mail address: [email protected] (F. Puertas). 0950-0618/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.conbuildmat.2013.07.008

different factors affecting the rheological behaviour of the cement. The physical parameters of cement pastes, which govern their characteristics and physical behaviour under different conditions can be studied on the grounds of their rheology [1–3]. In on-site concrete casting, the general trend is to use binders with a high solids content but low yield stress and viscosity. This combination ensures high performing concretes with no detriment to their workability. Since viscosity and yield stress are generally agreed to be exponentially related to the water/cement ratio, the conditions for obtaining an ideal compromise between solids content and paste fluidity need to be determined [4]. That objective can be attained by controlling both the physical–chemical characteristics of cement pastes and the inter-particulate forces with the addition of superplasticisers to the mix [5–9].

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Mineral additions are used in cement for economic and environmental reasons, as well as to enhance mortar or concrete strength and durability. Mineral additions reduce the amount of clinker needed in Portland cement manufacture. In other words, their presence lowers the high temperature (and energy consumption) required and also mitigates other adverse impacts of cement manufacture. The economic and environmental advantages of the use of this type of cements have fuelled their use the world over. Of the 27 types of common cements listed in European standard EN197-1, 26 contain some manner of mineral addition (such as limestone, fly ash, blast furnace slag, silica fume or burnt shale). The mineral additions chosen for the present study were limestone and fly ash, both listed in European standard EN197-1. Their effect on paste rheology constituted the object of the research conducted. Limestone-blended cements have been widely studied. Their durability and mechanical strength are similar to the values found in the non-blended cements, and compressive strength remains high at replacement ratios of up to 25% [10–16]. Another mineral addition used in cement compositions is pozzolanic aluminosiliceous fly ash, whose presence in cement has beneficial effects, such as higher late-age mechanical strength. It also affords improved concrete durability by constraining the expansion associated with the reaction between the aggregate and the alkalis in cement [17– 20]. Since the use of these mineral additions may also alter paste rheology [5,7,8], further studies are needed to through more light on the subject. The use of mineral additions has been generally thought to improve end product performance, although it has negative effect on the workability [21,22]. The main reason given for such behaviour is that the large specific surface of these fine powders generates a high water demand. This effect is observed primarily when silica fume is the mineral addition used. It is not always present, however, when other mineral additions are chosen. The literature has reported that some mineral additions lower water demand and raise slump [2,4,11,23,24]. Improved workability and lower water demand in fly ash-blended cements is attributed to the fact that its spherical particles can readily roll over other particles, reducing inter-particulate friction and raising paste fluidity [4,22,25,26]. In limestone-blended cements, however, no consensus has been reached on the effect of the addition on paste fluidity. Some authors have observed improvements in rheological properties, especially yield stress, plastic viscosity and water demand [8,23,27], while others have found cement rheology to be adversely affected by limestone [21,28]. A number of authors [5,8,21,29] studying the effect of superplasticisers admixtures on cement paste rheology, have reported that the adsorption of part of the admixture onto the mineral additions in blended cements alters their behaviour and ultimately their effect. In other words, the rheological behaviour of fresh cement directly affects the microstructure development and strength behaviour of mortars and concrete. In light of the foregoing, the present study focuses on the joint effect of mineral additions (limestone or fly ash) and superplasticisers on cement paste viscosity and water demand and the concomitant impact on microstructure and strength.

Table 1 Chemical composition (%,weight) and Blaine fineness of the cement and additions used. % p.

CEM I 52.5R

L

FA

L.O.I. SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 SO3 Sireact Blaine (m2/Kg)

2.35 20.51 5.37 2.10 0.02 3.86 57.05 0.64 1.44 0.16 0.13 6.37 – 501.7

43.56 0.34 0.04 0.11 0.01 0.93 54.56 0.36 – 0.01 0.08 – 0 –

6.76 46.32 31.01 4.50 0.05 1.29 4.90 0.34 1.34 1.53 0.98 0.98 36.4 –

1.22 1.19 7.08 22.46

4.38 0.81 3.58 35.14

2.70 1.80 13.81 59.33

ESBET (m2/g) Dv(lm)

10 50 90

Table 2 Density values of CEM I 52.5R and blended cements. CEM

Density(g/cm3)

I 52.5R

10L

30L

50L

10FA

30FA

50FA

3.15

3.05

2.97

2.93

3.00

2.78

2.60

Table 3 Physical and chemical characteristics of the admixtures used. Admixture

PNS

PMS

PCE

Solid content (%) Mw (Da) Mn Rotational viscosity (mPas) %C %S %H %N Na (ppm) K (ppm) pH

39.6 136,995 25,695 51.11 43.78 9.13 4.53 0.80 31,400 340 8.5

41.9 78,828 7315 31.50 18.65 10.65 3.98 22.17 55,280 0.2 8

40.9 59,596 35,923 118.20 51.67 0.30 8.14 0.17 2820 10 4.5

Three commercial superplasticisers admixtures were also added: a naphthalene-based (PNS), a melamine-based (PMS) and a polycarboxylate-based (PCE) product. Their physical-chemical characteristics are given in Table 3.

2.2. Methodology 2.2.1. Paste rheology Cement paste rheological behaviour was determined with a Haake Rheowin Pro RV1 rotational viscometer fitted with a grooved Z38S (Haake) cylindrical rotor to avoid slippage. Behaviour was studied with different solids contents. The solids content in a cement paste, defined as its volume fraction ð/Þ, is related to the water/cement (w/c) ratio as shown in following equation:

/ ¼ ðqw =qc Þðw=c þ ðqw =qc ÞÞ

ð1Þ

2. Materials and methodology 2.1. Materials The study was conducted with CEM I 52.5 R commercial Portland cement (hereafter CEM I) and limestone (L) and fly ash (FA) mineral additions. The chemical composition and specific surface of the materials are listed in Table 1. Six blended cements were prepared in the laboratory with CEM I and 10, 30 or 50 wt% limestone or fly ash and respectively labelled CEM 10L, CEM 30L, CEM 50L, CEM 10FA, CEM 30FA and CEM 50FA. Each cement was blended in a mixer for 2 h. Table 2 lists the densities of the cements used.

where qw and qc are water and cement density, respectively. The cement pastes were prepared by mixing 100 g of cement and the amount of water established for each trial with a mechanical blade stirrer for 3 min. Six milligram of PNS and PMS polymers/g cement and 2 mg of PCE polymer/g of cement were added to the mixing water (the optimal dosages were determined in an earlier study) [5]. In the rheological tests, the cement pastes were subjected to pre-shear at 100 s-1 for 1 min, return to a rotor velocity of 0 s-1, re-ramping to 100 s-1 in 12 min and lastly a gradual reduction in speed to 0 s-1 in a further 12 min. The downward shear rate values were fit to the Bingham equation (Eq. (2)), in which the y-intercept

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O. Burgos-Montes et al. / Construction and Building Materials 48 (2013) 417–423 determines the yield stress (s0) and the slope of the regression line the plastic viscosity of the paste (g). In all cases the rheological curves exhibited the same behaviour and the downward arm of the shear rate curves fit the Bingham equation: :

s ¼ s0 þ gðcÞ

3. Results and discussion 3.1. Paste rheology Cement paste behaviour is determined by physical–chemical inter-particle and particle–medium interaction. The tendency of cement particles to agglomerate and form floccule detracts from their flowability. The degree of agglomeration depends on the nature, composition and size of the cement particles, as well as the water content in the medium. Fig. 1 shows the variations in plastic viscosity (determined in the rheological tests) with the solids volume fraction for the CEM I 52.5R pastes, in the presence and absence of superplasticisers. In Portland cements, viscosity (g) is related to the solids content expressed as volume ð/Þ according to the Krieger–Dougherty equation [30]:



2.0

½g/m ð3Þ

where gc is viscosity in the continuous phase, /m is the maximum solids content by volume and [g] is intrinsic viscosity. The Krieger–Dougherty equation describes the effect of solids content on cement suspension viscosity (g). The maximum solids content depends on particle shape and particle size distribution. The maximum solids content can be calculated empirically by measuring the viscosity of pastes with different solids contents [31] and then fitting the results to calculate the theoretical curve. Due to the very diverse size distribution and shape of the particles in the cements used in the present study, however, the experimental data proved to fit the Krieger–Dougherty equation very poorly. When fitted mathematically, they exhibited an exponential curve in all cases. Nonetheless, for CEM I that exponential pattern was observed to concur with the Krieger–Dougherty equation predictions. The exponential nature of the curve was an indication that cement pastes with over a given maximum solids content were not fluid. With the addition of superplasticisers which, as expected, raised the maximum solids content value, pastes could be prepared

Viscosity (Pa·s)

ð2Þ

2.2.2. Paste strength and microstructure Prismatic specimens measuring 1  1  6 cm were prepared with CEM I and blended cements, CEM 10L, CEM 30L, CEM 50L, CEM 10FA, CEM 30FA and CEM 50FA with the w/c ratio found in rheological trials for viscosity 1.5, as described in Section 3.1 below and shown in Fig. 3. The pastes were mixed as described in European standard EN-196-1 in an Ibertest 32-040E mixer. Each mould was filled with two lifts of cement and dropped 60 times on the flow table after each lift was cast. The specimens were chambercured at 22 °C and 99% relative humidity for 24 h and subsequently removed from the moulds and stored in a humidity chamber until the test time (2, 7 or 28 days). Compressive strength was determined at the test ages on an Ibertest Autotest 200/ 10 hydraulic test frame as specified in Spanish and European standard UNE-EN 1961. Unblended CEM I 52.5R paste strength, found under the same conditions as the strength for the experimental materials, was adopted as the control. In other words, the strength for blended pastes with no superplasticiser was compared to the CEM I 52.5R paste strength with no superplasticiser, while the strength for the pastes prepared with PNS or PCE was compared to the strength observed for CEM I 52.5R pastes with the same superplasticiser. One 28-day specimen of each type of cement was immersed in acetone to stop the cement hydration reactions and subsequently vacuum-dried. Total porosity and pore size distribution of cement pastes were determined by means of a Micromeritics Autopore IV 9500 analyser. Additionally the morphology of the 28-day CEM 50L and CEM 50FA pastes was studied under a Hitachi S-4800 Scanning Electron Microscope (SEM/EDX).

g / ¼ 1 gc /m

2.5

1.5

1.0

0.5

0.0 0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

Solids volume fraction Fig. 1. Apparent viscosity versus solids volume fraction for CEM I 52.5R pastes in absence and presence of admixtures.

with lower w/c ratios. For each cement, the maximum solids value is known as the maximum solids content ð/max Þ. Of the admixtures used, PCE lowered water demand most effectively, while only minor differences in performance were found between PMS and PNS. The variation in paste viscosity with the solids content (/) was determined for the limestone- and fly ash-blended pastes in much the same way as for the reference cement. The respective maximum / values were obtained by extrapolation from the maximum viscosity values on the exponential curves obtained for cements used. Entering this value in Eq. (1) yielded the w/c ratio required to ensure the maximum viscosity in each paste. The minimum w/c ratio found for the pastes (i.e., the minimum amount of water that must be added for the pastes to flow with maximum viscosity), with and without superplasticiser, is plotted against the amount of mineral addition in Fig. 2. As Fig. 2 shows the water demand was lower in the pastes prepared with superplasticisers than in the reference samples. For up to 30% limestone admixtures, the variations in the w/c ratio were fairly insignificant, in both the absence and the presence of superplasticisers. When the limestone replacement ratio reaches 50%, however, the minimum w/c ratio declined substantially (Fig. 2 above)The reduction in water demand in the 50 L limestoneblended cement pastes containing superplasticisers was 31% for PNS and PMS and 33% for PCE, compared to a 26% decline in the paste with no superplasticiser. The beneficial effect of limestone on the w/c ratio was attributed to the size and dispersion of its particles (Table 1), able to occupy small voids between cement particles [11]. When up to 30% fly ash (10FA and 30FA) was added to the cement (Fig. 2 below), the minimum w/c ratios declined slightly in the pastes containing PSN and PMS. The pastes prepared with PCE, by contrast, exhibited a significant drop in water demand with 30% fly ash. The addition of up to 30% fly ash was more effective than limestone in lowering water demand. This may be due primarily to the spherical morphology of the ash articles, which would reduce inter-particulate friction and therefore raise paste fluidity [21]. Blends with 50% fly ash also lowered the water demand and improved the fluidity of the cement pastes. The decline without superplasticisers was 40%, compared to 37% with PNS and PMS and 39% with PCE. Here, the superplasticisers proved to be less effective when the paste contained 50% fly ash [8]. The general performance pattern of the superplasticisers in fly ash-blended cement was similar to the pattern observed for the limestone blends, however, with PCE providing for the steepest decline and PNS and PMS exhibiting identical effectiveness. Under minimum w/c

O. Burgos-Montes et al. / Construction and Building Materials 48 (2013) 417–423

0.50

0,50

0.45

0,45

water/cement ratio

water/cement ratio

420

0.40 0.35 0.30 0.25 0.20

0,40 0,35 0,30 0,25 0,20

0.15

0,15 0

10

20

30

40

50

0

10

Limestone (%) 0.50

water/cement ratio

water/cement ratio

0.35 0.30 0.25

0.35 0.30 0.25 0.20

0.15

0.15 20

30

50

0.40

0.20

10

40

Without admixture PNS PMS PCE

0.45

0.40

0

30

0.50

Without admixture PNS PMS PCE

0.45

20

Limestone (%)

40

0

50

Fig. 2. Minimum w/c ratio determined for each paste at maximum viscosity value.

conditions, the scant availability of water may favour floc formation in the pastes, yielding scarcely workable materials. Further to the present findings, the viscosity value established for suitable workability was 1.5 Pas. The w/c ratios found for each paste (with and without mineral additions and superplasticisers) are shown in Fig. 3. As the figure shows, the variation in paste w/c ratio at 1.5 Pas was similar to that found for their maximum viscosity (see Fig. 2). With 50% limestone and PNS and PMS, water demand was 15% lower than in the pastes with no superplasticiser, while with PCE the difference was 24%. Water content also declined when fly ash was added, by 16%, 20% and 21% with PNS, PMS and PCE, respectively. Under 1.5 Pas viscosity conditions, which were less demanding than maximum viscosity, the difference between the effects of limestone and fly ash was smaller. When viscosity was 1.5 Pas the w/c ratios were higher and solids content consequently lower. As a result, the stabilising effect of the fly ash particles was not as effective as at higher solids content values. Therefore, the presence of the mineral additions studied affects cement paste rheology, in particular water demand. The inclusion of less than 30% limestone did not alter substantially the paste w/c ratio. In pastes prepared with 50% limestone, however, water demand declined substantially. The presence of up to 30% fly ash reduced the water demand slightly. As for limestone, when the fly ash content was 50%, the w/c ratio declined substantially. When the proportion of mineral addition was high, at 50%, the w/c ratio dropped to nearly half. In all the cements studied, the effect of PNS and PMS superplasticizers barely differed, while PCE was the superplasticiser that most effectively reduced mixing water demand.

10

20

30

40

50

Fly ash (%)

Fly ash (%)

Fig. 3. Minimum w/c ratio determined for each paste at a viscosity value of 1.5 Pa s.

3.2. Paste strength and microstructure One of the determining factors in paste, mortar and concrete microstructural development is the water/cement ratio used in their preparation. Microstructure, in turn, determines the permanent strength and durability of these materials. As the above rheological tests showed, the presence of mineral additions and different types of superplasticisers altered the minimum w/c ratio for a given viscosity. The effect of the minimum water/cement ratios on the variations in cement paste strength and paste microstructural development in the presence and absence of superplasticisers are discussed in this section. Because of the similarity of PNS and PMS performance, only PCE and PNS were used in these tests. The 2-, 7- and 28-day compressive strength of limestone- and fly ash-blended cement pastes with no superplasticiser admixture, with PNS and with PCE were determined for given w/c ratios and a constant viscosity value of 1.5 Pas. The strength activity index (SAI) was found with Eq. (4) below to determine the effect of the mineral additions on paste strength:

SAI ¼

Blended cement strengh Reference cement strength

ð4Þ

A coefficient greater than one therefore means that the mineral addition raised cement strength, while values of less than one denote lower strength in the blended cement than in the control. The SAI values for each age studied are plotted against the proportion of limestone addition in Fig. 4. At all ages, the pastes prepared with 10% limestone and no superplasticiser exhibited higher strength than the unblended

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2 days

1.4 1.3

0.8 0.7 0.6

PCE PNS

PCE

No PNS PCE

PNS

No

0.9

15

PCE

1.0

PNS

% Cumulative

1.1

No

20

1.2

S.A.I.

Microporous (< 0.01 µm) Mesoporous (0.05 - 0.01 µm) Macroporous (10 - 0.05 µm) Air Porous (> 10 µm)

25

Without admixture PNS PCE

No

1.5

10

5

0.5 10L

30L

50L 0

1.5

7 days

1.4

CEM I

10L

30L

50L

Fig. 5. Pore size distribution (in lm units) in limestone-blended pastes at 28 days curing.

1.3

S.A.I.

1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 10L

30L

50L

1.5

28 days

1.4 1.3

S.A.I.

1.2 1.1

Fig. 6. SEM micrograph of 28 day-CEM 50L pastes.

1.0 0.9 0.8 0.7 0.6 0.5 10L

30L

50L

Fig. 4. SAI values for limestone-blended pastes at 2, 7 and 28 days of curing.

cement. In general, the pastes with higher limestone contents and either PCE or PNS had SAIs of less than one, an indication that here the addition of limestone had no beneficial effect on strength, despite the lower w/c ratio observed. The Hg porosimetry findings (Fig. 5) showed a decline in total porosity and pores with a size higher than 0.05 lm in limestoneblended pastes, which was steeper in the presence of a superplasticiser. The pore size distribution underwent no substantial change, however, in the presence of either rising amounts of limestone or superplasticisers. These results may be interpreted as follows: limestone, given its particle size and texture (see Table 1), favours workability. That, in conjunction with its capacity to adsorb superplasticizers [5], would explain the decline in paste w/c ratios. Since this material also acts as a filler, its presence would lower paste porosity.

The SEM micrograph of the 28-day sample of CEM 50L reproduced in Fig. 6 shows that the limestone particles form an integral part of the paste matrix, generating a very compact microstructure. None of these developments induced a significant increase in strength, for the ultimate effect was not associated with the formation of more cohesive products, but only with physical events (better particle distribution and dispersion and more compact structures). Fly ash-blended cement strength was affected primarily by two factors: a refinement of particle size and type (as in the case of limestone) and the reaction induced by its pozzolanic activity. The former effect would be reflected to a greater extent at early ages, whereas the pozzolanic effect would appear at later ages. The variation in SAI with the proportion of fly ash in the cements is shown in Fig. 7. The cements with 10% fly ash and no admixture had SAI values of over one. At early ages, 2 and 7 days, the ashblended cements with superplasticisers had lower strength than the unblended cement, with the exception of CEM10CV with PNS. The bearing strength of 28-day cements with 10% and 30% fly ash rose as a result of the pozzolanic reactions and the formation of more reaction product (essentially C–S–H gels). This rise was steeper in the pastes containing admixtures, which exhibited values of nearly 1. The SAI of the paste with 50% fly ash was the lowest at all the ages studied, for two reasons: on the one hand, the dilution effect induced by the mineral addition and on the

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O. Burgos-Montes et al. / Construction and Building Materials 48 (2013) 417–423

1,5

2 days

1,4

Without admixture PNS PCE

1,3

S.A.I.

1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 10FA

30FA

50FA

1,5

7 days

1,4

Fig. 8. SEM micrograph of 28 day-CEM 50FA pastes.

1,3 Microporous (< 0.01µm) Mesoporous (0.05-0.01µm) Macroporous (10-0.05 µm) Air porous (> 10µm)

25

1,0

0,5 10FA

30FA

50FA

1,5

1,3

0

1,2

S.A.I.

No No PNS PCE

PCE

No

10

5

28 days

1,4

15

PNS

0,6

PNS PCE

0,7

% Cumulative

0,8

PNS

20

0,9

PCE

1,1

No

S.A.I.

1,2

1,1

CEM I 52.5R

10FA

30FA

50FA

Fig. 9. Pore size distribution (in lm units) in fly ash-blended pastes at 28 days curing.

1,0 0,9 0,8 0,7 0,6 0,5 10FA

30FA

50FA

Fig. 7. SAI values for fly ash-blended pastes at 2, 7 and 28 days of curing.

other the high proportion of unreacted fly ash, for the amount of water in these cements was very low in comparison to the amount of ash present, preventing the pozzolanic reaction in many of the particles. This effect was verified by SEM: note the large number of cenospheres in the micrograph of the 28-day CEM50CV sample reproduced in Fig. 8. Fig. 9 shows paste porosity for different amounts of fly ash. The pastes containing 50% fly ash and superplasticisers had a higher porosity than the other samples, which would explain their lower strength. The pastes with no superplasticisers and 10% fly ash exhibited lower porosity, while at higher proportions of mineral addition, porosity increased. This would be explained by the large amount of unreacted ash, whose presence would yield a microstructure with scant particle packing. In conclusion, adding 10% limestone or fly ash improved cement strength considerably. Strength declined in cements with 30% and 50% limestone because the smaller proportion of cement generated

less reactive phase. When fly ash was added at a rate of 50%, strength declined because the scant amount of water available during hydration limited the effect of the pozzolanicity of the addition. The use of mineral additions reduced the effectiveness of cement superplasticisers. 4. Conclusions The main conclusions drawn from the results of this study are listed below: (a) Krieger–Dougherty equation could be used to determine the effect of solids content on the apparent viscosity of limestone- and fly ash-blended cement suspensions, as well as the effect of superplasticisers. (b) Adding limestone to cement at proportions of under 30% had little effect on paste rheology. The w/c ratios for minimum and optimal workability were similar to the ratios for ordinary cement. When 50% of the cement was replaced with the mineral addition, the water demand was lower. (c) Adding fly ash lowered the minimum water demand and the optimal amount of water for suitable fluidity. (d) As expected, the use of superplasticisers lowered the water demand in all the cements. The PCE-based superplasticiser induced the steepest declines.

O. Burgos-Montes et al. / Construction and Building Materials 48 (2013) 417–423

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