Construction and Building Materials 23 (2009) 609–614

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Construction and Building Materials

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Review

Influence of coal bottom ash as fine aggregate on fresh properties of concrete

L.B. Andrade, J.C. Rocha *, M. CheriafDepartment of Civil Engineering, Federal University of Santa Catarina, Florianópolis-SC 88040-900, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:Received 24 August 2007Received in revised form 25 February 2008Accepted 6 May 2008Available online 26 June 2008

Keywords:ConcreteCoal bottom ashFresh propertiesBleedingPlastic shrinkage

0950-0618/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2008.05.003

* Corresponding author. Tel.: +55 4837215169; faxE-mail address: janaide@ecv.ufsc.br (J.C. Rocha).

This paper investigates the influence of the use of coal bottom ash as a replacement for natural fine aggre-gates on the properties of concrete in the fresh state. Tests for water loss through bleeding, and the deter-mination of the setting times and plastic shrinkage, were carried out in order to evaluate the material inthe presence of bottom ash. The influence of the porosity of bottom ash on the potential water absorptionand water loss of the material, as well as on the water consumption of concretes produced with bottomash, is also discussed. The results showed that in the fresh state the concretes produced with the bottomash are susceptible to water loss by bleeding and the higher the percentage of bottom ash used as a nat-ural sand replacement the lower the deformation through plastic shrinkage. The results also showed thatthe setting time is affected by the presence of bottom ash in the concrete. In conclusion, different forms ofbottom ash mix result in concretes with different properties in the fresh state, but the behavioral tenden-cies are maintained when bottom ash is employed as a replacement for natural aggregates.

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6092. Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6103. Experimental program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6104. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611

4.1. Bleeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6114.2. Setting time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6114.3. Heat evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6124.4. Plastic shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613

5. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614

1. Introduction

Results reported in the literature are promising regarding theuse of bottom ash as a partial or total fine aggregate replacementfor natural sand [1–6]. Thermoelectric power stations produce agreat quantity of residues from burning coal [1–4]. These residues,mainly fly ash and bottom ash, have a very effective potential usein mortar and concrete.

Due to the high porosity of coal bottom ash, there is a certaindifficulty in determining the exact water/cement ratio. Thus, manyassumptions are based on an estimated quantity of water whichdoes not participate in the processes of material lubrication and

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the filling of void spaces. This water present inside the bottomash grain through capillary retention, would not contribute tothe formation of capillary pores [7–10]. Although the waterabsorption by the bottom ash alters the water intended for theworkability of the concrete, this effect makes it act as a porousaggregate functioning as a reservoir of water for future hydrationof the cement [5,6,11–14]. The plastic shrinkage of the concreteis directly affected by the quantity of water available in it, whichmay be lost through bleeding (settlement), changing the relativehumidity and the internal capillary pressure [15–18]. The use ofa porous material which can promote a supply of water internallyto the concrete, without permitting that there is an excessive cap-illary attraction force, makes the system less susceptible to defor-mations or cracking through plastic shrinkage, which is of greatinterest.

0

20

40

60

80

100

0.0 0.1 1.0 10.0Grain-size (mm)

Acc

umul

ated

frac

tion

(%)

Natural sand (NS) 25% BA/NS 50% BA/NS75% BA/NS Bottom ash (BA)

Fig. 1. Grain size distribution curves for bottom ash/natural sand (BA/NS) mix.

610 L.B. Andrade et al. / Construction and Building Materials 23 (2009) 609–614

This paper presents the results of a study using bottom ash incommon concretes as a replacement for natural sand, analyzingthe performance in fresh state regarding bleeding, setting time,heat evolution and plastic shrinkage.

2. Materials

� Cement. The cement used was CPV – ARI (high initial resistance),according to the Brazilian standard NBR 5733/91 (similar to typeIII ASTM C 150-05). Table 1 shows the chemical and physicalcharacteristics of the cement used.

� Natural fine aggregates. A natural siliceous sand was used, classi-fied within the optimum zone according to the Brazilian stan-dard NBR 7211/2005, with a specific mass of 2.63 g/cm3 and afineness modulus of 2.50.

� Natural coarse aggregates. A granite gravel was used, classifiedwithin the range 9.5/25.0 (d/D), according to the Brazilian stan-dard NBR 7211/2005, with a specific mass of 2.70 g/cm3 and amaximum size of 19 mm.

� Bottom ash. Collected from the settling pond of the Jorge Lacerdathermoelectric power station, which generates 840,000 tons ofbottom ash annually, in Santa Catarina, southern Brazil. Thechemical and physical characteristics are given in Table 1.

The chemical composition of the bottom ash was analyzed byX-ray energy dispersive spectrometry (EDS). The calcium contentis very low (2.07%) and the sum of SiO2 + Al2O3 + Fe2O3 reaches89.5%, which means that this ash belongs to ASTM Type F ash. Ina previous study [7], the chemical composition of this bottomash was investigated by ICP and ICP-AES and it was found to con-tain MgO (0.6%). The sum CaO + MgO content is very low <1.4%.

The grain size distribution of the bottom ash and natural sandare shown in Fig. 1 and the scanning electron micrograph in Fig.2. All of the natural sand replacement was carried out by volume,adding bottom ash in the same volume as the natural sand.

3. Experimental program

The concrete mixes were prepared according to two forms ofbottom ash addition: (a) equivalent volume replacement,correcting bottom ash quantities according to the moisturecontent – CRT3; (b) non-equivalent volume replacement, withoutreplacement of bottom ash according to the moisture content ofthe aggregate – CRT4.

Table 1Chemical and physical characteristics of Portland cement and bottom ash

Content (%) Cement Bottom ash

Chemical analysisSiO2 18.13 56.0Al2O3 4.28 26.70Fe2O3 2.54 5.80K2O – 2.60CaO 59.80 0.80TiO2 – 1.30SO3 3.14 0.10Na2O – 0.2MgO 5.25 0.60CaO free 1.47 –Loss on ignition 3.29 4.6

Physical testsBlaine (cm2/g) 4.098 –Initial setting time (h:min) 1:30 –Final setting time (h:min) 2:37 –Specific gravity (g/cm3) 3.12 1.674

The second form of proportion (CRT4) enabled the maintenanceof mechanical properties, based on the results obtained for the ref-erence concrete with 100% of natural sand. However, to achievethis, a greater quantity of cement was required, due to the lowerquantity of fine aggregates per volume of concrete.

Table 2 shows the consumption of the material of the concreteswith bottom ash. The workability was specified for a slump of80 ± 10 mm. The fresh density was determined by the gravimetricmethod. The test for water loss by bleeding was carried out in acontrolled temperature room at 22 ± 2 �C and 60 ± 5% relativehumidity. The water was collected from molded samples in a glasscontainer with an exposed area of 140 � 190 mm2 using a syringeto hold the water removed without small particles. The evaluationof the bleeding was carried out for a period long enough to collectwater from the surface of the sample. When between two mea-surements no quantity of water was collected the test was consid-ered completed. Zero time was counted from the time of placingthe sample in the test container. One minute before each readingthe container with the concrete samples was inclined at an angleof approximately 15�, promoting the positioning of surface wateron one side of the container to facilitate its collection. The waterwas collected at 12-min intervals, long enough to deal with severalsamples simultaneously.

The setting time of the concrete was determined under thesame ambient conditions as the bleeding test, and simultaneouslywith the plastic shrinkage test. The measurements were carriedout according to the French standard NF EM 196-3 (1990), usingthe test apparatus with a Vicat needle adjusted to receive an extramass of 700 g, ensuring that the needle was not blocked by fineaggregate grains. The evaluation of setting was carried out aftersieving of the concrete in a sieve with an open mesh of 4.8 mmto remove coarse aggregates. The measurement of heat evolutionin mortar samples with the same composition as the concrete,except for the presence of coarse aggregates, was carried out usinga semi-adiabatic calorimeter [19,20]. The temperatures werecollected using type-K thermocouples, and stored in a Data Loggerconnected to a PC. The plastic shrinkage test consisted of monitor-ing the linear deformation of a prismatic sample of 70 � 70 �500 mm3. Immediately after concrete manufacture, the samplewas taken to a climatic chamber for molding in the plastic shrink-age monitoring equipment. The equipment for the measurement ofdeformation consisted of an LVDT – Linear Variable DifferentialTransducer, fixed to a metal plate in contact with the concretesample. This plate was fixed to the sample by four screws insertedinto the fresh concrete. The plastic shrinkage measurement wascarried out through the displacement of the metal plate. The LVDTwas connected to a signal amplifier which downloaded the data toa Data Logger coupled to a microcomputer.

Fig. 3. Apparatus for the test for plastic shrinkage of concrete.

Fig. 2. SEM of a porous bottom ash particle in concrete.

Table 2Mix details of bottom ash concrete

Concrete Mix proportion (kg/m3) Fresh density (kg/m3) BA moisture (%)a Compressive strength (MPa)

Cement Sand BA Gravel Water 3 days 28 days 90 days

0% CRT 304 912 0 806 219 2238 – 15.9 28.4 32.025% CRT3 305 686 145 808 277 2177 50.0 12.5 23.2 25.750% CRT3 301 452 287 798 336 2090 50.0 9.9 18.0 23.075% CRT3 295 221 422 782 373 1964 52.0 6.3 11.5 14.9100% CRT3 299 0 570 792 378 1869 57.0 4.2 8.6 12.525% CRT4 323 727 103 856 245 2220 50.0 19.5 27.2 32.150% CRT4 334 501 212 885 272 2138 50.0 17.0 28.5 35.975% CRT4 356 267 340 943 303 2109 50.0 16.1 26.1 32.7100% CRT4 386 0 441 1023 323 2040 67.0 21.2 32.6 38.4

a Water content present in the bottom ash at the time of testing.

L.B. Andrade et al. / Construction and Building Materials 23 (2009) 609–614 611

The plastic shrinkage equipment is composed of Plexiglas platesto avoid absorption by the mold and water leakage from the sam-ple. The mold was covered externally with metal plates to avoidlateral deformation of the concrete in its initial state. Fig. 3 showsthe plastic shrinkage equipment. The test was started immediatelyafter the time of the onset of the concrete setting, when the lateralplates were removed from the mold.

The mechanical tests for the determination of the compressivestrength and deformation modulus were carried out on concretespecimens molded into cylindrical forms of 100 mm diameterand 200 mm height, cured in a laboratory environment for 24 hand afterwards in a humid chamber (24 �C and 95% RH) until thetest age. Three specimens per age were tested for each concrete.

4. Results and discussion

4.1. Bleeding

After concrete has been manufactured and molded the processof segregation begins due to the different weights of the constitu-ent materials. The aggregates and particles of the cement tend tooccupy the points closest to the bottom of the container whereasthe water tends to be displaced to the top. This rising of the wateris called bleeding. Three factors are of great importance for theconsiderations made regarding the influence of bleeding on theperformance of the concrete: (1) the quantity of water which is lostby bleeding and that which evaporates to the environment towhich it is exposed, since the greater the quantity of water whichleaves the interior of the concrete the greater the tendency toward

problems of durability in relation to the transport properties (cap-illarity, permeability) in the hardened state; (2) the total time forwhich the water bleeding occurs, since the longer the bleedingtime the less significant the capillary pressure due to the dryingof the pores will be; (3) the bleeding rate, measured in water massloss per exposed area over time [21,22]. This factor provides animportant value which can be related to the surface evaporation,where a lower bleeding rate value in relation to the evaporationrate results in the start or continuity of the plastic shrinkage pro-cess [23–26].

As can be seen in Fig. 4, the type CRT3 concretes have greaterwater in the mix/cement of the concrete (w/c) ratios and have ahigher rate of water loss by bleeding, and the greater the bottomash content the higher these values become. The type CRT4concretes showed a similar behavior, however, with values muchcloser to the reference concrete, that is, with natural sand. It isclear that the increase in the w/c ratio greatly influences the re-sults, but the rate of the release of water from the interior ofthe bottom ash also contributes to the increase in the bleedingvalue.

The values for water loss in relation to total water were close forthe contents of 25% and 50%, for both CRT3 and CRT4 types of con-crete (Fig. 5). However, it can be noted that this loss increases withbottom ash content due to the increase in the total quantity ofwater present in the mixes (75% and 100%).

4.2. Setting time

The initial setting time is the moment characterized by an in-crease in the temperature of the concrete after the dormant period

Table 3Initial and final setting time

Concrete (%) Initial setting (min) Final setting (min)

0 230 330

CRT3 25 250 36050 340 47575 350 460100 270 540

CRT4 25 240 34050 210 31575 225 315100 195 255

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 40 80 120 160 200 240 280 320 360

Time (min)

Ble

edin

g ra

te (k

g/m

2 /h)

0% 25% 50% 75% 100%

CRT4

0 40 80 120 160 0 40 80 120 160 200

CRT3

Fig. 4. Rate of water loss by bleeding during the test period.

0

3

6

9

12

15

0% 25% 50% 75% 100%

Bottom Ash Content

Wat

er lo

ss/to

tal w

ater

(%)

CRT 3 CRT 4

Fig. 5. Water loss by bleeding in relation to total water added in the mix.

612 L.B. Andrade et al. / Construction and Building Materials 23 (2009) 609–614

and also the moment at which the mix begins to show a certain le-vel of stiffness. This initial stiffness is of great importance for theconcrete to bear the tensile force caused by the plastic shrinkage,if the concrete element has a physical restriction, for example,crimping which prohibits a dimensional variation, without therebeing cracking. Thus, delays in the time at which setting startsmay reduce the durability – with the appearance of cracks – of con-cretes subject to plastic shrinkage with physical restrictions. Onthe other hand, if the setting starts earlier, together with a longerbleeding time, this can be beneficial in the prevention of deforma-tion and cracking through plastic shrinkage. Some studies haveidentified that the addition of bottom ash to cement materials in-creases the initial and final setting time, in relation to the referencemix [4]. This is due to the increase in the quantity of water presentin the mixes with bottom ash, resulting in the maintenance of agreater workability, consequently, increasing the time that themix is in the fresh state, due to a greater distancing of the cementhydration products. Another factor is the possible reduction of thepH of the medium, which causes a delay or decrease in the hydra-tion activities of the cement particles [9].

Table 3 shows the results for the setting time of the concreteswith bottom ash. The performance of the CRT3 type mixes wascharacterized by considerable delays in the initial and final settingtime. This is in contrast with the CRT4 concrete mixes for whichthe setting process was accelerated, with the exception of a con-tent of 25% for which it was a little longer than the referencemix. In the CRT4 mixes, the reduction in the setting time in relationto the reference mix was low since, in these concretes the totalwater consumption did not correspond to the reality of the quan-tity of water released to the mix, even being slightly higher, sincesome of the water present internally in the bottom ash is not re-

leased to the mix in the fresh state, as stated above. For this reasonthe hydration dynamics, and as a consequence the setting dynam-ics, of the CRT4 concretes did not differ greatly from the referencemix.

This fact cannot be verified for CRT3 concretes, since the quan-tity of water consumed in relation to the reference mix was consid-erably higher. Thus, a high quantity of free water in the mix willlead to mixes with a tendency toward longer setting times. Itwas found that the content of 100% in the CRT3 concrete was thatwhich gave the longest final setting time, 540 min. The same con-tent but in the CRT4 concrete was that which gave the shortesttime of all of the mixes manufactured. For both mixes, the contentof 25% resulted in values very close to each other and to the refer-ence concrete.

Even though the type CRT3 concretes showed longer times forthe initial setting, the values for the deformation by plastic shrink-age were not greater due to the high quantity of water loss bybleeding and its consequent storage on the surface of the concrete.This inhibits an excessive evaporation and keeps the internal watercontent of the mix sufficiently high so that the capillary pressure isnot too high.

4.3. Heat evolution

The temperature increase is a direct result of the heat involvedin the cement hydration. The cement hydration reactions are exo-thermic, and the heat released is dependent on the characteristicsof the cement, ambient temperature and the thermal characteris-tics of the system. Each event in the hydration process is accompa-nied by heat evolution. The values measured are the integral heatvalues covering all of the reactions going on in the setting andhardening of the mixes based on Portland cement: wetting heat,heat of the solution of the individual constituents, hydration ofions transferred to the solution, precipitation or crystallizationheat, reaction of new hydrates formed in the mix [27].

The mixes of the three series, with lower quantities of cement,had peak temperatures lower than those of the four series con-cretes, according to Fig. 6. The three series also showed a delayfor the maximum temperature peak to be reached in relation tothe reference concrete, in agreement with the data obtained forthe setting test with the Vicat needle, except for the CRT3 25% con-crete. This did not occur in the case of series 4 concretes, which hadshorter times for the maximum temperature peak to be reached inrelation to the reference concrete. This explains the advance in thetime for the onset of setting for this series in relation to the refer-ence, in the mechanical test. The maximum temperature peaks forthe CRT4 concretes were all higher that that of the reference con-crete, and the higher the peak the greater the bottom ash content,with the exception of the CRT4 100% mix.

Due to the greater cement content, the CRT4 series showed agreater heat evolution over time than the reference concrete. Ofthe two series, a greater evolution of heat was also found for series

Fig. 7. Evolution of heat for series CRT3 and CRT4.

Fig. 9. Plastic shrinkage deformation after initial setting time of bottom ash conc-rete – CRT3.

Fig. 6. Temperature evolution in the test for series CRT3 and CRT4. Fig. 8. Rate of heat involved for series CRT3 and CRT4.

Fig. 10. Plastic shrinkage deformation after initial setting time of bottom ashconcrete – CRT4.

L.B. Andrade et al. / Construction and Building Materials 23 (2009) 609–614 613

4, as shown in Fig. 7, even though the quantity of heat was greaterfor series 3, in J/g, than for the reference sample.

For the heat evolution shown in Fig. 7, the bottom ash contentresulted in a greater heat development for a greater replacementlevel, except for the 25% and 50% contents of the CRT3 series,where there was an inversion of this tendency, with a greateramount of heat for the 25% content in relation to the 50%.

As can be seen in Fig. 8, the heat evolution rate (J/g h) showedthe same tendency described above, that is, for the CRT4 seriesthe higher the replacement content, in relation to the referenceconcrete, the higher the peaks. Likewise, in the CRT4 series, thereis an inversion of the heat evolution rate tendency for contentsof 25% and 50%.

4.4. Plastic shrinkage

The phenomenon of plastic shrinkage in concrete is presentedin this paper through monitoring over time the longitudinal lineardeformation of the prismatic specimen. This phenomenon, despitebeing reported in a number of publications, has been under discus-sion in recent years. Some researchers attribute the phenomenonto environmental causes of water loss by bleeding [28,29]. Morerecently, advances in the understanding of the phenomenon havedeepened our scientific knowledge of the main cause of concreteplastic shrinkage: an excessive force of attraction in the pores,caused by the water loss, measured by the increase in capillarypressure [15,16,30–32].

The use of a porous aggregate which enables the supply ofwater after the molding and compression of the mix may be em-ployed as a preventative measure to avoid the plastic shrinkage.However, in this study, the role of the bottom ash as a water reser-

voir was not the only factor involved in the reduction in plasticshrinkage. A considerable increase in the quantity of water lossby bleeding, and the consequent bleeding rate and total bleedingtime, contributed significantly to the reduction in plastic shrinkageof the concrete with bottom ash.

According to Figs. 9 and 10 and Table 4, it can be observed thatthe CRT3 concretes, which have greater w/c ratios, had lower plas-tic shrinkage values. This is due to the effect, previously explained,of the high water bleeding which is driven by the high water con-sumption of CRT3 type concretes. However, the CRT4 type con-cretes had higher plastic shrinkage values in relation to thereference concrete since the consumption of cement is higher, this

Table 4Maximal plastic shrinkage deformation

Concrete (%) Maximal deformation(mm/m)

Time to maximal deformationafter initial setting time (h)

0 0.031 2.7

CRT3 25 0.015 6.850 0.009 10.075 0.009 1.8

100 0.013 10.0

CRT4 25 0.005 7.850 0.088 6.275 0.088 4.1

100 0.065 3.5

614 L.B. Andrade et al. / Construction and Building Materials 23 (2009) 609–614

being a direct result of the differentiated proportioning or non-equivalent replacement of the bottom ash.

For the CRT3 type concretes the plastic shrinkage deformationshowed little variation even considering that the quantity of waterloss by bleeding was very high when the bottom ash content washigh. This was also observed for the CRT4 type concretes.

In relation to plastic shrinkage, it can therefore be inferred thatthe presence of bottom ash has a significant influence. This can beattributed not only to the higher water content of the concrete butalso to the effect of it acting as a water reservoir, since the CRT4concretes with greater contents of bottom ash showed close val-ues, even though the cement consumption increased with in-creases in bottom ash content.

5. Conclusions

According to the analysis of the results and discussion, the fol-lowing conclusions may be drawn:

� The high porosity of the bottom ash means that the w/c ratio ofthe concrete cannot be taken as exact. The water absorbed inter-nally by the bottom ash is released to the concrete over time,being part of the production process with the concrete still inthe fresh state.

� The presence of bottom ash increased the quantity of water lossby bleeding, the bleeding time and also the water release rate,and the higher the bottom ash content of the concrete thegreater this effect.

� Delays in the initial and final setting time in relation to the ref-erence concrete were observed for the CRT3 type concretes dueto the higher quantity of bottom ash and lower quantity ofcement.

� The data for the hydration heat test for the concretes with bot-tom ash revealed a slight delay for the maximum temperaturepeak to be reached for the mixes of series 3, which have a higherquantity of bottom ash in relation to series 4 for the same con-tent of replacement material, due to the way the material wasadded in the mixes. However, the samples of the CRT4 seriesgave higher accumulated temperatures and also greater quanti-ties of heat produced, along with a higher rate of heat evolution.The reference concrete showed a lower quantity of heat evolu-tion as well as a lower heat evolution rate in relation to the con-cretes with bottom ash.

� The results for the plastic shrinkage test confirmed the influenceof the high water content in the CRT3 concretes and of theincrease in the consumption of the CRT4 cement. In the first casethere was a decrease in the total deformation due to the greaterbleeding; in the second case the value for the final deformationdue to plastic shrinkage increased due to the lower quantity ofaggregates, and consequently greater chemical shrinkage dueto the greater quantity of cement particles available.

� The two ways to add bottom ash in the concrete mixes influ-enced significantly the mechanical behavior. The CRT3 typeconcrete, due to the high w/c ratios, showed very significantlosses in compressive strength. The CRT4 type concretes, whichwere manufactured with the aim of maintaining the mechanicalproperties, gave similar results to those of the referenceconcrete.

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