P073 2003-05

TMS Journal December 2005 73

1 Auxiliar Professor, Department of Civil Engineering, University of Porto, Portugal, [email protected].

2 Associate Professor, Department of Civil Engineering, University of Porto, Portugal, [email protected].

3 Industrial Manager, Maxit, pavimentos e Blocos S.A., Albergaria-A-Velha, Portugal, [email protected].

Methodology for the Design of Lightweight Concrete with Expanded Clay Aggregates

Ana M. Bastos1, Hipólito Sousa2, and António F. Melo3

Figure 1— Examples of Precast Products Made with Lightweight Concrete

In Portugal, lightweight expanded clay aggregates (LECA) are typically used in the production of vibrant-compressor lightweight concrete, which presently repre-sents 10% of the total volume of vibrant-compressor con-crete produced in Portuguese factories. The use of LECA aggregates has increased since it was introduced in 1990’s, after the acquisition of the Portuguese factory by the in-dustrial word leader of LECA production [Melo (2000)].

Lightweight expanded clay aggregates are still pro-duced at that Portuguese factory, by the same process as the one used in other European factories, and with similar chemical characteristics (Table 1) [Pöysti, M. and Geir Norden, G. (2000)].

Vibrant-compressor lightweight concrete is mainly employed on precast products, usually masonry blocks and lightweight units for slabs (Figure 1). In Portugal, the most popular masonry materials are clay units, large and horizontally perforated, used on enclosure and internal walls [Sousa (2000)].

In European countries, practices related to light-weight concrete for the manufacture of masonry blocks are similar, and different from other concretes:

• It is produced in special vibrocompressor systems (Figure 2), by strong vibration and compression;

• The cement content is usually low, according to the desired strength, to minimize the cost and to limit shrinkage;

• The quantity of water is low to allow blocks extru-sion immediately after moulding without slump;

• The use of superplasticizers, air-entraining and anti-efflorescence agents is not usual, at least in south Europe countries.

Important factors affecting the final properties of these concretes are the grading and mechanical strength of the aggregates, the mix proportions, the type of block machine and the curing process [Bresson J. and Brusin (1974)].

Lightweight concrete expanded clay aggregates ex-hibit particular properties: favourable thermal and acoustic

Table 1. Chemical analysis of LECA aggregates used in the study SiO2 Al2O3 Fe2O3 TiO2 MgO CaO

46.6% 14.5% 6.6% 0.6% 3.0% 17.7%

Na2O K2O MnO P2O5 Rest<0.1% 3.4% 0.2% 0.2% >7,1%

behaviour provided by the volume of voids, although with low mechanical strength. For structural use, it is normal to incorporate ordinary aggregates in the concrete mix to achieve adequate mechanical strength [Moyer (1986) and Crestois (1986)].

Until recently, the design of lightweight concrete mixes has been based upon the experience and knowl-edge of the vibrant-compressor systems manufacturers. Research on these lightweight concrete mixes is limited

Figure 2— Vibro-Compressing System

74 TMS Journal December 2005

because of the difficulty of reproducing, in the laboratory, production conditions related to moulding of specimens of sizes typically used for defining concrete properties. With the increasing use of lightweight concrete with expanded clay aggregates in precast products for construction, there is a need for a better understanding of for the properties of these concretes in order to more effectively design and optimize the characteristics of these products.

The aim of experimental work presented is to develop and calibrate a methodology to relate mix design of vi-brant-compressor lightweight clay aggregate concrete with the needed and expected densities of the concrete [Melo (2000)]. As with other lightweight concretes, the most im-portant properties of vibrant-compressor lightweight clay aggregate concrete are related to concrete density.

Because the properties of LECA aggregates are simi-lar to those produced at other European factories, and because the specification of the cement (in accordance with Portuguese and European standards [NP EN 197-1 (2001)]) used in the different locations is consistent, the results of this study can be applicable to other factories of LECA products.

This research was conducted under a research project between the main Portuguese factory of these products and the Engineering Department of Porto University.

EXPERIMENTAL STUDY

Planning

The experimental program consists of the design and characterization of seven lightweight concretes with densities between 853 and 1,418 kg/m3, which represent values currently used by the masonry blocks industries. To analyze the influence of cement content on concrete properties, four different quantities of cement were used for each of the seven mix design groups.

Dry bulk density, compressive and flexural strengths, elastic modulus, shrinkage, and absorption capacity by immersion and by capillarity and thermal conductivity were experimentally determined. The development of concrete compressive strength with age was also evalu-ated, by tests starting from ages of 1 day up to 160 days.

Concrete Mix Design

The first methods for the design of concrete mixes were fully empiric, based on mortar production tradition-ally used, following fixed rules independent of the nature of the components, which guaranteed high compactness with superabundance of binder [Dreux (1986)].

In the 20th century Feret (1888), Fuller (1907) and Leclerc du Sablon (1927) developed experimental methods for testing a large number of mixtures. Later Faury (1958), based on the work of Bolomey (1930) and Caquot (1937), proposed a combined aggregates and cement grading curve, that includes the influence of the vibration conditions, the shape of the particles, the wall effect and the water/cement ratio, in order to achieve the maximum compactness of the solid components. Other reference curves were presented by Joisel (1952) and Vallette (1963), but the one defined by Faury is most often used [Dreux (1986)]. Other methods based upon pre-defined concrete mixes using aggregates with standard grading curves are also used.

Faury’s reference curve (Figure 3) is a discontinuous combined (aggregates and cement) grading curve, that in-cludes the influence of the vibration conditions, the shape of the particles and the wall effect (discontinuous distribution of the large particles of aggregate in mould if the maximum size of aggregate is large in relation to the size of the mould [Neville (1973)]), to achieve maximum compactness.

52 17

0 75D /

BP A DR .D

= + +−

(1)

1 1 - 2

xD d (d d )y

+=

(2)

5K K'I

BD 0.75D

= +−

(3)

PD/2 = Cumulative percentage passing of material with size under D/2

A = Faury parameter related with the nature and shape of the aggregate and the vibration energy

B = Faury parameter depending on workabilityD = Maximum aggregate sizeI = Voids index of a compact concrete including wa-

ter addedK = Faury parameter related with the nature and shape

of the aggregate and the vibration energyK′ = Faury parameter depending of workabilityR = Mould medium radius (quotient of the volume of

concrete by the surface of the mould) related with wall effect

d1 = greatest size of the sieve where is a retained fractiond2 = next sieve to d1

The xx-axis scale, between 6.5 μm (minimum size of cement grains) and D, is proportional to the fifth root of the sieve size. The yy-axis scale is linear representing the cumulative percentage of the material passing.

The design of the percentages of aggregates and ce-ment in the mixture must lead to a grading of the com-


Figure 3— Faury’s Reference Curve

bined aggregates similar to the reference curve in order to obtain maximum compactness for the group of aggregates concerned and considering real conditions of workability and vibration.

This is achieved with the following conditions:

• the fineness modulus of the mix should be as close as possible as the one of the reference curve,

mo = m1 p1 + m2 p2 +... + mn pn (4)

with p1 + p2+….+ pn = 1 (5)

m0 = fineness modulus of reference curvem1,…mn = fineness modulus of aggregates 1, …, np1, …pn = percentage of aggregates 1, …, n in the mix

• the medium quadratic deviation between the ref-erence curve and the mix curve should be mini-mum;

• the adjustment of concrete density can be achieved replacing a light aggregate for a normal aggregate with the same grading [Melo (2000)].

These methods have only been applied for the de-sign of traditional concrete mixes. Nevertheless, it seems reasonable to apply the Faury’s method to lightweight concrete, by experimental adjustments in order to obtain desired values of the density or strength. The values of the mix design parameters must be consistent with the speci-fications of the production process [Melo (2000)]: very strong vibration, high wall effect and workability of very dry concrete.

Aggregates and Cement characteristics

The following aggregates were used in mix composi-tions:

• coarse aggregate of expanded clay, LECA (of 4 mm < d < 10 mm), from LECA Portugal;

• fine aggregate of expanded clay, LECA (size 0 - 2 mm), from LECA Portugal;

• coarse normal aggregate, crushed granite (of 4 mm < d < 10 mm), from granite stone quarry;

• fine normal aggregate (maximum size 0-2 mm), natural granite sand.

Information on the characteristics of aggregates is summarized in Table 2.

The current aggregates, sand and crushed granite, show grading curves similar to those of LECA (4-10) and LECA (0-2), respectively. The adjustment of concrete density was achieved by partial or total replacement of lightweight aggregate by normal aggregate with equal volume of LECA of the same size in order to maintain an approximately constant fineness modulus. The cement used was Portland cement II 42.5R, in accordance with Portuguese and European standards.

Mix Proportion of Lightweight Concretes

Seven lightweight concretes (D1 to D7, Table 3) with densities between 853 and 1,418 kg/m3 were produced. The seven concrete mixes (D1 to D7) used four different amounts of cement, 126, 155, 185 and 214 kg/m3 (D1A to D1D).


Information on mix proportions and concrete expect-ed dry bulk density are summarized in Table 3.

The application of Faury’ method to the design of one of the mixes (mix D2C) is shown in Figure 4.

For production of lightweight concrete with expanded clay aggregates, the amount of water in the mix is automat-ically determined after the measurement of water content in the aggregates. No chemical admixtures were added.

EXPERIMENTS

Specimens Production and Curing

The specimens for the different characterization tests of the mixtures, with sizes according to the applicable In-ternational Standards, were moulded in a metallic mould specially designed for utilization at the vibrant-compres-sor systems (Figure 5).

Table 2. Aggregates CharacteristicsCoarse aggregates Fine aggregates

Characteristics Lightweight “LECA 4-10”

Normal cr. granite

Lightweight “LECA 02”

Normal natural sand

Specific gravity (kg/m3) 540 2,730 1,320 2,650Loose bulk dry density (kg/m3) 330 1,420 660 1,510Compacted dry bulk density (kg/m3) 350 1,540 730 1,650Water absorption capacity (% by weight) 18.8 0.9 18.1 0.2Crushing strength (N/mm2) 1.04 _ _ _D-maximum aggregate size (mm) 10.06 8.04 2.42 2.38Fineness modulus 5.39 5.17 2.82 1.91Average moisture content in production con-ditions (% by weight) 27.7 3.8 31.0 5.3

The number and size of the cubes, cylinders and prisms required for testing are summarized in Table 4. The specimens used for the compressive strength tests were also utilized for the evaluation of the dry bulk den-sity of the mixes.

Each test mixture was produced on the same day, with the same aggregates, and in one of the factory machines, under similar conditions in which the masonry blocks are produced, to assure the vibration parameters and mould-ing time of real production.

All the industrial systems had been previously calibrat-ed. The mixer has an automatic system to adjust water add-ed considering the moisture in aggregates. The aggregates were pre-soaked in order to achieve saturated conditions.

The samples were placed in trays and clearly marked. The storage and transport to the curing chamber was done by an automatic system.

Figure 4—Design of Mix D2C by Faury’s Method


Table 3. Mix Design Adopted

Mix Cement( kg/m3 )

LECA 4-10( % )

LECA 0-2

( % )

Gravel( % )

Sand( % )

Dry bulk density

( kg/m3 )D1A 126 70 20 10 853D1B 155 70 20 10 853D1C 185 70 20 10 853D1D 214 70 20 10 853D2A 126 70 10 20 960D2B 155 70 10 20 960D2C 185 70 10 20 960D2D 214 70 10 20 960D3A 126 70 30 1,067D3B 155 70 30 1,067D3C 185 70 30 1,067D3D 214 70 30 1,067D4A 126 65 5 30 1,155D4B 155 65 5 30 1,155D4C 185 65 5 30 1,155D4D 214 65 5 30 1,155D5A 126 60 10 30 1,243D5B 155 60 10 30 1,243D5C 185 60 10 30 1,243D5D 214 60 10 30 1,243D6A 126 55 15 30 1,330D6B 155 55 15 30 1,330D6C 185 55 15 30 1,330D6D 214 55 15 30 1,330D7A 126 50 20 30 1,418D7B 155 50 20 30 1,418D7C 185 50 20 30 1,418D7B 214 50 20 30 1,418

Figure 5—Mould Used for Specimen Production

300 x 300

d=100

d=100

180 x 220

200 x 200

200 x 200

200 x 200

200 x 200

200 x 200

200 x 200

700

x 10

0

700

x 10

0

700

x 10

0


All specimens were cured under the same conditions, 8 days in a climatic chamber where the temperature was maintained at 14ºC and the relative humidity was 90%. After this 8-day period, the specimens were placed in a shelter with no temperature or humidity conditioning.

Test procedures

The moisture content of fresh concrete (difference, in percentage, between moisture and dry mass of samples af-ter seven days drying in a climatic chamber with tempera-ture of 75ºC and the workability by Vebe test [ISO 4110 (1980)] were determined for the mixes produced. Com-pression strength testing [NP EN 12390-3 (2003)] at 28 days on cubic specimens was carried out. Three point load bending tests [E227 (1968)] were undertaken at 28 days on prismatic specimens in order to evaluate tensile strength. Young’s modulus [E397 (1993)] as well as compression strength were determined at an age of 36 days, on prismat-ic specimens, for seven reference mixes, D1B to D7B.

The evolution of concrete compressive strength with age was determined by compression tests at 26 hours, 3, 7, 14, 28, 59, 91, 120 and 160 days for three reference mixes, D1B, D4B, D7B (6 specimens per age and mix).

Shrinkage measurements [E398 (1993)] were under-taken on two specimens of each of the same three reference mixes above, starting from 23 hours up to 120 days; for that period the specimens were kept in a climatic chamber at 21ºC and relative humidity of 55%. Measurements of the displacements were obtained by using an analogical transducer (with resolution of 1310-3 mm.

Water absorption by immersion [E394 (1993)], dur-ing a period of 210 days, and by capillarity [E393 (1993)], starting from 1 hour up to 15 days, were evaluated for the same three reference mixes, D1B, D4B, D7B.

Table 4. Tests and Specimen

Test Dimensions of Specimens (m) Number of Specimens/Mix

Dry bulk density Cylinder d = 0.10 h = 0.20 6Compressive strength 0.20 x 0.20 x 0.20 6Tensile strength in bending 0.10 x 0.20 x 0.70 (t x h x l) 3Young’s modulus 0.10 x 0.10 x 0.30 (v x h x l) 31

Concrete compressive strength evolution with age 0.20 x 0.20 x 0.20 542 Shrinkage Cylinder d=0.10 h=0.20 22 Water absorption by immersion 0.10 x 0.10 x 0.10 (t x h x l) 12 Water absorption by capillarity 0.10 x 0.10 x 0.20 (t x h x l) 12

Steady state thermal transmission 0.30 x 0.30 x 0.05 (t x l x h) 11 t = thickness; h = height; l = length 1 made for seven selected mixes 2 made for three selected mixes

The Guarded Hot Plate Method [NP116 (1962)] was carried out to evaluate thermal conductivity of concrete, at the age of 240 days, for the seven mixes (D1b to D7b). The specimens for tests were covered by a thin layer of sulphur to achieve full contact with the hot and cold plates of the testing equipment.

EXPERIMENTAL RESULTS AND DISCUSSION

Workability and Moisture Content of Fresh Concrete

The workability of the fresh concrete obtained by Vebe test, appropriate for very dry mixes, was approxi-mately 4 seconds, for the mixes produced, leading to a rough concrete without cohesion [NP ENV 206 (1993)].

Moisture content of fresh concrete obtained for each mix is presented in Table 5. The results show decreases in moisture content with decreases in the amount of light-weight aggregate used in mix composition, as is expected because of the considerable absorption capacity of light-weight aggregate.

Table 5. Moisture Content of Fresh Concrete

Mix Reference

Lightweight Aggregate

Content (%)

Water Content (% by weight of fresh concrete)

D1B 90 19.2D2B 80 15.8D3B 70 13.3D4B 65 12.9D5B 60 10.8D6B 55 10.2D7B 50 9.8


Concrete Dry Bulk Density, Strength and Young’s Modulus

The values of compressive and flexure concrete strengths and Young’s modulus for the different mixes as well as a comparison between the expected and effec-tive dry bulk densities [ISO 6275 (1982)] are presented in Table 6.

Faury’s reference curve method used for mix design could provide a good estimate for the dry bulk concrete density. The deviation between real and expected density values is usually negative leading to the necessity to in-crease the volume of fines to achieve the desired density

and reduce porosity. It should be noticed that some con-crete segregation with concentration of coarse aggregates on one side of the mould was observed, which could be responsible for the high deviation on mechanical concrete properties compared to those for concretes produced in moulding machines of modern factories.

The lower and upper limits on compressive concrete strength variation were 5.13 and 11.70 kN/mm2. Results showed an increase of compressive strength with the quantity of cement when low percentages of lightweight aggregate were used. For mixes with low quantities of ce-ment (mixes D1A to D7A) the compressive strength was less affected by the quantity of lightweight aggregate in the composition.

Table 6. Density and Resistance of Lightweight Concretes

Mix Reference

Dry Bulk Density Compressive Strength (at 28 days)

Tensile Strength in Bending (at 28 days)

Young’s Modulus (at 36 days)

Expected(kg/m3)

Real(kg/m3)

Deviation(%)

Mean Value

(N/mm2)

Variation Coefficient

(%)

Mean Value

(N/mm2)

Variation Coefficient

(%)

Mean Value

(N/mm2)

Standard Deviation(N/mm2)

D1A 853 836 -2.0 5.93 2 1.38 8 - -D1B 853 836 -4.2 5.63 6 1.49 10 5,400 0.5D1C 853 908 1.8 6.79 4 1.61 9 - -D1D 853 871 -5.0 5.39 15 1.76 2 - -D2A 960 870 -7.9 5.49 4 1.49 6 - -D2B 960 919 -4.2 5.53 7 1.35 21 6,800 1.5D2C 960 939 -4.6 6.26 9 2.07 7 - -D2D 960 1,003 0.6 6.56 9 2.06 8 - -D3A 1,067 988 -4.1 5.13 12 1.44 12 - -D3B 1,067 950 -10.5 6.93 6 1.84 8 7,900 0.9D3C 1,067 985 -8.3 6.80 12 2.24 7 - -D3D 1,067 1,096 1.0 8.19 9 2.40 14 - -D4A 1,155 1,035 -9.1 5.95 11 1.73 16 - -D4B 1,155 1,240 7.4 6.90 5 1.64 7 8,800 1.3D4C 1,155 1,199 2.8 7.48 7 2.23 8 - -D4D 1,155 1,136 -4.0 8.62 8 2.42 3 - -D5A 1,243 1,157 -4.5 6.65 7 1.80 6 - -D5B 1,243 1,209 -1.4 6.69 8 2.21 9 10,300 1.6D5C 1,243 1,178 -5.4 8.31 9 2.26 17 - -D5D 1,243 1,311 4.0 9.27 6 2.58 3 - -D6A 1,330 1,229 -7.9 5.83 13 1.78 11 - -D6B 1,330 1,285 -4.4 8.52 7 2.19 4 14,700 2.9D6C 1,330 1,312 -3.4 8.79 8 2.67 6 - -D6D 1,330 1,367 -0.4 10.64 4 2.68 6 - -D7A 1,418 1,330 -6.9 6.17 15 2.02 9 - -D7B 1,418 1,458 1.5 8.92 8 2.38 14 13,500 1.6D7C 1,418 1,443 -0.3 11.62 4 2.55 8 - -D7D 1,418 1,487 1.5 11.70 5 2.81 10 - -


Figure 7—Compressive Strength Evolution

Figure 6—Compressive Strength, Quantity of LECA and Cement Content

Concrete tensile strength in bending, while showing a higher variation coefficient, was shown to be dependent on the quantities of cement and lightweight aggregates. Tensile strength increased with the quantity of cement (maximum of 67% between reference mixes D3A and D3D, Table 6) and with decreases of lightweight aggre-gate (maximum of 49% between mixes D1 and D6).

The ratio between tensile and compressive strengths was 0.27 (average value), considerably above the ratios for normal concretes, which are approximately 0.08 for concretes grade C12 to C20 [Model Code 90 1991].

The characteristic value (minimum value obtained in 95% of specimens tested) of concrete compressive strength, the percentage of lightweight LECA aggregate, and the cement content are plotted in Figure 6.

The values obtained for Young’s Modulus and con-crete strength of lightweight concrete mixes with cement content of 155 kg/m3 (mixes D1-b to D7-B), at the age of 36 days, as well as density, are presented in Table 7. The limit

Table 7. Young’s Modulus of Lightweight Concretes

Mix Reference

Dry Bulk Density (kg/m3)

Compressive Strength(MPa)

Young’s Modulus

(GPa)D1B 836 4.50 5.43D2B 919 6.46 6.83D3B 950 6.06 7.93D4B 1240 6.58 8.77D5B 1209 7.22 10.33D6B 1285 7.63 14.73D7B 1458 10.36 13.53

values of Young’s Modulus are 5.4 and 14.7 MN/mm2. As expected, Young’s modulus increased with concrete strength and density (except for mix D7B).

The experimental values are 55% lower than those obtained by the equation proposed by ACI 318-89,

6 1 543 10 .

c cE fρ− ′= ×

(6)

Ec = concrete Young’s Modulus, in MN/mm2,f ′c = standard cylinder strength, in kN/mm2, ρ = concrete density, in kg/m3.

Evolution of Concrete Compressive Strength with Age

The evolution of concrete compressive strength at ages of 26 hours, 3, 7, 14, 28, 59, 91, 120 and 160 days on the three mixes, D1B, D4B, D7B, with the same amount of cement and with different densities (836, 1,240 and 1,458 kg/m3, respectively) is shown in Figure 7. Strength


evolution over the period of 160 days is identical for the three mixes. A maturity adjustment curve of the average strength, σmean, was developed (Figure 7) and it is a func-tion of the logarithm of age and the percentage (pla) of lightweight aggregate:

0 0038 1 033 0 0564 8 088mean la n la( . p . )l ( age ) . p .σ = − + − + (7)

Shrinkage

Lightweight concretes usually exhibit a high drying shrinkage. Because of the lower modulus of elasticity, lightweight aggregate offers less restraint to the potential shrinkage of cement paste [Neville (1973)]. Shrinkage evolution is presented in Figure 8. The shrinkage-time curves for the three mixes are similar, showing the up-per values for the mixes with greater percentage of light-weight aggregates.

Figure 8—Shrinkage Evolution with Time

The results show that, up to 28 days, 75% to 80% of drying shrinkage occurred and after 60 days shrink-age evolution almost stabilized. Early expansion can be observed for mix D7B, with higher percentage of normal weight aggregate.

Water Absorption by Immersion and Capillarity

Water absorption by immersion and by capillarity was evaluated for the three mixes, D1B, D4B, D7B, with per-centage of lightweight aggregates of 90%, 65% and 55%, respectively. The results are presented in Figures 9 and 10 showing the increase of water absorption by immersion and by capillarity with the percentage of expanded clay aggregates in mixes, as it should be expected by the high porosity of lightweight aggregate.

Figure 9—Water Absorption by Immersion of Different Mixes


Figure 10—Water Absorption by Capillarity

Thermal Conductivity

The ability of lightweight aggregate concrete mason-ry blocks to conduct heat is relevant to thermal insulation provided by walls, as a lower thermal conductivity will reduce heat exchange with the outside ambient.

Thermal conductivity by the hot plate method was obtained for four mix references – D2B, D3B, D4B and D7B. The comparisons between the thermal conductiv-ity, the dry bulk density, and the quantity of lightweight aggregate that are presented in Table 8, show an increase with concrete density [Sousa Coutinho (1988)]. Results obtained will permit the use of lightweight aggregate concrete masonry blocks on single leaf walls without any other thermal insulation materials, according to what is required by Portuguese codes [RCCTE (1999)].

CONCLUSIONS

The experimental study undertaken aimed to evaluate the applicability of a mix design method for lightweight clay aggregate concretes used to produce lightweight con-crete masonry blocks. The research aimed to forecast con-crete properties from mix composition and from density.

Table 8. Thermal Conductivity

Mix Reference

Dry Bulk Density(kg/m3)

LECA Content

(%)

Thermal Conductivity

(W/mºC)D2B 919 80 0.33D3B 950 70 0.44D4B 1,240 65 0.51D5B 1,209 60 0.48

Considering the results obtained, the following con-clusions may be drawn:

• Faury’s reference curve method seems to be ad-equate for concrete design due to agreement of the expected and real density. Relationships and influ-ences are found between the density, the LECA content and some properties of concrete.

• The limit values of compressive concrete strength are 5.13 and 10.7 kN /mm2, related to aggregate characteristics and cement content. Results show that, as long as the cement quantity is low, the pro-portions of lightweight or normal aggregate do not significantly influence the compressive strength, which is relatively low. When upper cement per-centages are used, the reduction of lightweight aggregate enhances the compressive strength. The evolution of compressive strength with age is sim-ilar to that for current aggregate concretes.

• The absolute value and the evolution of shrinkage are relevant parameters for masonry materials, as it may affect wall behavior, if the blocks are sent to site before the needed cure time. The results ob-tained are similar to the current values for light-weight products. Shrinkage evolution over time show that under normal conditions of cure, 75% to 80% of drying shrinkage has occurred and has almost stabilized at 60 days.

• Results obtained for the thermal conductivity of the multi-chamber masonry blocks enable their use on single leaf walls, with economical and techni-cal advantages related to more rapid construction and less dependent workmanship quality.


• Results of this study are likely applicable to other factories of LECA products.

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Caquot, A., “Le Role des Materiaux Inertes Dans le Bé-ton,” Mem. Soc. Ing. Civils de France, Vol. 90, No. 4, pp. 562 (in French) 1937.

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393 - LNEC, “Betão. Determinação da Absorção de Água por Capilaridade,” Portuguese Standard (in Por-tuguese), 1993.

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Joisel, “Composition des Bétons Hidrauliques,” Ann. Inst. Tech. Bat. Trav. Publ. (in French) 1952.

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Moyer, C., “Caractéristiques Thermiques des Betons Lé-gers,” Granulats et Betons Legers, Bilan de dix ans de recher-ches, Presses de l’École Nationale des Ponts et Chaussées, ed. M. Arnould, M. Virlogeux, (in French) 1986.

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NP EN 12390-3, ”Ensaios do betão endurecido. Resistên-cia à compressão dos provetes de ensaio”, Portuguese Standard (in Portuguese), 2003.

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Sousa, H., “Portuguese Masonry Building Enclosures. Practices and Problems,” CIB W23 Wall Structures- 37th. Meeting, August 23-24, Penn State, USA, 2000.

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NOTATIONS

A = Faury parameter related with the nature and shape of the aggregate and the vibration energy.

B = Faury parameter depending on workability.d1 = greatest size of the sieve where is a retained

fraction.d2 = next sieve to d1.D = maximum aggregate size.Ec = concrete Young’s Modulus, in MN/mm2.f ′c = standard cylinder strength, in kN/mm2.h = height.

I = voids index of a compact concrete including water added.

K = Faury parameter related with the nature and shape of the aggregate and the vibration energy.

K′ = Faury parameter depending of workability.l = length.m0 = fineness modulus of reference curve.m1,…mn = fineness modulus of aggregates 1, …, n.pla = percentage of lightweight aggregate.PD/2 = cumulative percentage passing of material

with size under D/2.p1, …pn = percentage of aggregates 1, …, n in the mix.R = mould medium radius (quotient of the vol-

ume of concrete by the surface of the mould) related with wall effect.

t = thickness.μm = minimum size of cement grains.ρ = concrete density, in kg/m3. σmean = a maturity adjustment curve of the average

strength.

Documents

P073 2003-05