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75

HYPOTHESI S FOR THE STUOY OF NEW BRICK PROOUCTS

GIORGIO CERAGIOLI

GIOVANNI CANAVESIO

FRANCESCO OSSOLA

Politecnico di Torino

Oipartimento di Casa Città

Dipartimento di Ingegneria dei Sistemi Edilizi e Territoriali

Viale Mattioli 39 - 10125 TORINO - ITALY

ABSTRACT

In relation to studies and research that have been carried out in the

domain of production and application problems of brick/block masonry ,

the authors work on the assumption of a " design line " to study new

products based on simplification of building processes as well as on

performance suboptimization of brick products in relation to a set of

performances easily adaptable according to the specific climatic

environment and application requirements .

INTROOUCTION

Research work and studies dealt with in the present paper followed up on

the results of a previous research work , that SI . TE . RICERCHE Srl of

Torino (Italy) had carried out for ROB Spa of Piacenza (Italy) . Such

results had in fact generated some general assumptions that applied to

specific bui l ding requirements typical of industrialized countries :

need to simplify building processes in order to facilitate employment

of less skilled labour and favour self- construction by building

users ; need to suboptimize brick size performance in relation to production

processes and construction systems so as to achieve low energy­

content production meeting standard quality specifications;

need to produce brick products meeting a wide range of performance

specifications , easy to adapt and optimize in relation to different

sets of performance requirements (e.g . different combinations of

insulation and thermic inertia) , widening their range of use in

76

different climatic environments and applications.

The present brick masonry market partly satisfies to these needs through

some products such as those that are used in "construction systems" ,

integrating basic elements (blocks) with special components , t h us

ensuring technological building homogeneity and/or improving integration

with other sections of the building. Other recently introduced examples

are "guided-fit" elements featuring significant dimensional accuracy ,

that can be dry- built and then set by casting materiais through t heir

specific hollow sections. Other issues, however , such as specific

material structure and the development of its performance an d functional

specifications do not seem to attract due interest . In particular , the

extremely interesting and still very open issue remains of the as ­

sumption that , on average , brick products feature a "performance

surplus " in relation to present construction systems and/or ap ­

plications. This is not such a surprising statement when one considers ,

for instance, the significant strength surplus of a face brick in a

building with reinforced concrete skeleton. Its implications are

certainly relevant to the creation of new lines of brick masonry

products. The first of them is clearly a "targeted" decrease of some

spefications (basica l ly the highest surplus ones) so as to achieve

significant benefits in terms of cost and other issues (e . g . lower

energy consumption in production) . The second consideration , partly

following upon the first , is the need to design brick products f eaturing

different layers , each meeting a different requirement , so as to certify

each layer according to application- specific requirements . This would

ensure product "quality" through a much more in- depth and adequate

relationship between application "requirements" and product

" specifications" or,

" benefit" ratio.

in other words, through a more balanced "cost"-

HYPOTHES IS FOR A NEW PRODUCT

Following alI this, it is possible to assume and research a new line of

brick products consisting of large-sized tiles featuring a large centre

hollow section ready to be fi l led with whatever layer of material best

suits requirements . Such tiles mus t be easily juxtaposed by either dry

method or using binders to build perimetral and some times also inside

walls, so that , once the erection is completed, the centre hollow

sections may be filled with materiaIs meeting the specific functional

requirements of that construction work. Some suboptimizations are thus

feasible , since , even where minimum strength sections are used , this

brick product retains its resistance against externaI agents , thus

supplying the structural base or "she ll". .l\t the same time , i t is

possible

building

filling

to funct ionally design the construction process according

requirements and constraints through an adequate selection

materiaIs , which are e asier to f i nd locally, and that may

to

of

be

..

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77

either lower cost or lower energy- content products , though they still

meet the specified masonry requirements .

BASIC ELEMENT SPECIFICATIONS

The reference element upon which a first set of theoretical assessments

was ma de consists of a large block (Figure 1) featuring the following

specifications :

. / 3 standard tile, specific weight 1800 Kg m ;

dimensions:

- seam cutting span = 24 cm. ;

- maximum extrusion = 49 cm. ;

- minimum extrusion = to be determined (according to an analysi s of

the different application requirements providing performance

suboptimization) ;

externally pierced tile walls (piercing percentage around 50%),

thickness 4 cm.;

cross inner wa ll - connecting baffles reduced to minimum section needed

to provide adequa te strength;

edges shaped so as to facilitate juxtaposition , interlaying mortar or

~onding agent , or dry building.

Hollow section filling is assumed , in t his initial hypothesis, to use:

a) insulating materiaIs:

1) polysterene foam in situ;

2) urea resin foa m in situ ;

3) e xpanded pearlite aggregate ;

4) light expanded clay aggregate (LECA);

b) other aggregate materiaIs:

5) dry sand;

6) dry graveI;

7) natural pumice;

8) foamed slag ;

c) concrete mix castings:

9) expanded clay concrete;

10) standard concrete .

It is hardly worth stressing that, when standard concrete is used as

filling mater ial, tile hollows take on the typical function as "lost"

formwo rk elements where skeleton pillars are cast, or as elements suited

to antiseismic "reinforced masonry" construction. Expanded clay concrete

castings may also be used in this last application ( provided the

relevant static checks are carried out first) .

externally pi ere ed tile wall

241 em

78

. e ros s inner wall - eonneeting

Figure 1 . Basic block element with hollow section

~

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79

THEORETICAL ASSESSMENT OF PERFORMANCE

Performance of the range of solutions for perimetral walls built by

filling the basic brick element with the above mentioned materials may

be firstly assessed by focusing on the two basic specifications taking

into account stationary and variable heat transmission: unitary

Transmi ttance K (1) and Thermal Time Constant T o T o C o (2) , the latter

being adopted as significant parameter of thermic inertiao Theoretical

results of such initial assessment, supplying fairly clear- cut

information despi te i ts conciseness , are reported in Figure 2 , where

performance has been calculated in relation to overall brick element

thickness from 17 to 37 cmo and surface finishing consisting of outer

plastic plaster and inner cement plaster (overall wall thickness between

20 and 40 cm o ) o

With reference to such assessment, the following should be taken into

account :

1) The purpose of thickness variance is clearly to provide information

upon which to select the most adequa te thickness of the element (to

be finally defined wh en going into production) to meet assumed

application requirements through its range of filling alternativeso

2) Selection of outer plaster type is rather significant, since it must

ensure adequate waterproof features, which cannot be expected from

the 4cm o- thick basic brick element outer layer alone o

3) "Condensate forming " has also been checked, though i t is less

relevant an information than Transmittance and Thermal Time Constant :

it is in fact the result of anomalous environmental conditions , and

it can be avoided by selecting specific filling materials or it can

be controlled by fitting in a specific layer (which can be an outer

layer) o

4) " Thermal bridges", however, raise a problem the solutions to wh ich

have only been partially explored : at the present stage , however ,

some interesting indications point out new construction thermal

bridge- control specifications , which are in fact based on the h ollow

section of the brick element o

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81

CONCLUSIONS

These proposed new brick elements provide some general indications for a

new line of products , saving further in- depth research and operational

testing .

a) Possibility of integrated "dimensioning" of thermal performance by

building walls , for instance , with low Transmittance and Thermal Time

Constant values (or, on the contrary, with high values) , i.e .

relating insulation to thermic inertia according to the climatic

environment of the building (3) , something that is very hard to do

when using other one - purpose application potential technologies .

b) Possibility of achieving different performance values in walls f acing

different environmental climatic conditions, implementing, for

instance , lower transmittance in North- facing walls and highe r

thermic inertia in South-facing walls (since they get more summer sun

radiation). AlI t h is can be achieved by changing the material f il ling

the two walls, without changing the brick element o

c) Possibility to use filling materiaIs such as sand or graveI wh ich,

lacking thermal insulation requirements, are very suitable for Iow­

cost construction appIications, sir.ce they are generally:

- easiIy avaiIabIe 10caIly,

- low- cost ,

- very low energy- content.

d) Achievement of optimum insulation and thermic inertia vaIues (see

Figure 2) by means of specific filling materiaIs , such as pumice ,

featuring low thermal conductivity together with an apparent much

larger absolute gravity than that of typical insulating materi aIs .

With reference to pumice , there is t he additional a dvantage of using

natura l material that is extractible and usable through relatively

low- cost and very l ow energy- content processes.

e) Weight r eduction of brick elements produced , bringing about possible

ergonomic benefits , since construction using lighter (and larger)

elements provides better " construction performance", i . e . masons

raising a larger wall surface by unit of time ; this is however a

debatable indication , since filling must follow raising with the

re l evant additional times taken .

Final l y , it is interesting to see how , among the materia I s that can be

used to fil l the brick element hollow section , light expanded clay

aggregate (LECA) allows for high performance leveIs (also with regard t o

thermic inertia) with minimum wall overall thicknes s of 40 em . Th i s is

a rather interesting thing, since clay can be defined as a brick works

type of material . Further investigation may outline suboptimization

leveI s to be ac h ieved through adequa te granulometric selection with the

possible a ddition of sand (filling gaps between clay aggregate grains) ,

thus improving Thermal Time Constant , though at the expense of a

restrained increase in Transmittance.

(1)

(2)

82

NOTES

2 Unitary Transmittance K, expressed in w / m °c , is the heat f10w

going from one f1uid to another through a wa11 under stationary

conditions , mu1tip1ied by wa11 surface sq. mt . and °c of difference

between t he temperature of the two f1uids (UNI 7357 . Ca1cu1at i on of

therma1 requi rement for bui 1d ing heating) .

Therma1 Time Constant, expressed in hours , is the ratio

thermic energy stored in the wa11 per degree of increase

average temperature Qa , and heat f10w K* transmitted per

difference in t he temperature , both r eferred to the front

of the wa11 itse1f . For a wa11 consisting of N 1ayers:

Q

N a.

1 TTC i~l K*

i

where Q 2 p. s cp . (kJ/m °C)

a 1 i 1 i

between

in its

unit of

surface

With reference to Ki ' if t h e 1ayer sequence se1ected is inner to

outer , Ki is the f 10w going through to the i - th Iayer mid section ,

so that :

[ ~" s s s ::J I 1 2 i - 1 1 (m

2 °C/W) + - + - + ..... + -

K* À 1 À, À 2 i i - l

(3) See " Guida aI controllo energetico della progettazione" (Guide to

energy control in design), white book on results achieved in

relation to Subproject "Energy saving in building heating " of the

Energy Finalized Project of the Italian National Research Council .

AIso see Appendix 4 : "Consigli progettuali per l 'edificio e per

I ' impianto . Indicazion i di 15 Iocali tà i taliane " (Design

suggestions for the building and the heating system. Instances from

15 Italian sites) .

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