Upload
naa-korkoi-solomon-ayeh
View
223
Download
2
Embed Size (px)
Citation preview
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 1/29
K.A.Solomon-Ayeh
Structures, Building design and Planning Division
CSIR-BRRI
Kumasi
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 2/29
IntroductionAbout 90% of modern, masonry buildings in urban areas
of Ghana require the use of Ordinary Portland Cement(OPC)/Portland Lime Cement(PLC) for:
concrete ;
sandcrete + pavement blocks and bricks;
jointing;
plastering and screeding; tiling.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 3/29
Increasing housing stock and other infrastructuredemands increase use of cement and otherbinding(cementitous) materials, however:
Use of OPC/PLC imply;
increased importation of clinker
increased mining of limestone (from Buipe,
Otekpelu, Nauli)
high cost of input raw materials
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 4/29
Solution
Use of Clay Pozzolana as additive toOPC/PLC
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 5/29
Advantages
Clay fairly abundant inalmost every district ofGhana.
Requires relatively cheapstart up capital.
In presence of lime has
cementitious properties,among others.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 6/29
Engendering small
production units in
almost every district
Employment
Increased housing
stock
Increased rate Increased purchasing
power
of construction
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 7/29
Properties desired of hardened
cement mortar and concrete High compressive strength
Durability
Economic
Portland Clay- pozzolana cement when
used in concrete should achieve these to make it worthwhile.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 8/29
Chemical and Mechanical properties
of Portland clay-pozzolana cementProduction of OPC/PLC
Main components of Portland cement:
C3S Silicates, main cementitious compounds
C2S
C3A
C4AFhydration
SILICATES + WATER C-S-H gel + LIME
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 9/29
Beneficial and unbeneficial products
of hydration Beneficial product – C – S – H gel
Unbeneficial by-products:
(i) Free and combined lime
(ii) Magnesia
(iii) Calcium sulphate
(i), (ii), (iii) when react with water may expand andcause unsoundness of concrete.
(iii) by formation of ettringite
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 10/29
Clay pozzolana as binderClay pozzolana sequestrates lime to form acementitious material which, in addition to
OPC/PLC improves binding property of Portlandclay- pozzolana cement, among other usefulattributes.
slow
CLAY POZZOLANA + FREE LIME
C – S – H gel
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 11/29
Level of cementation depends on:
- Mass of Free lime available to sequester;
- Type of pozzolana;
- Amount of pozzolana present.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 12/29
Beneficial structural properties of concretesand rendering mortars made from Portland clay-
pozzolana cement.1. Strength
- Designed mixes to C12, C25, C40
- Part replacement of Portland lime cement byclay pozzolana at 0, 10, 20, 30, 40, 50% by wt.
- Complete immersion in water.
- Test of compressive strength at 7, 28, 120 days
Designed mix ratios, slumps and compressivestrengths are shown in Table 1.0 and Figs. 2,3 and4.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 13/29
0
2
4
6
8
10
12
14
16
0 20 40 60 80 100 120 140
C o
m p r e s s i v e s t r e n g t h ( M P a )
Age(days)
Fig. 2 - Compressive strengths for C12 concrete
0POZ:100PLC
10POZ:90PLC
20POZ:80PLC
30POZ:70PLC
40POZ:60PLC
50POZ:50PLC
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 14/29
0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
C o
m p r e s s i v e s t r e n g t h ( M P a )
Age(days)
Fig.3 - Compressive strengths for C25 concrete
0POZ:100PLC
10POZ:90PLC
20POZ:80PLC
30POZ:70PLC
40POZ:60PLC
50POZ:50PLC
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 15/29
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100 120 140
C o m p r e s s i v e s t r e n g t h ( M P a )
Age(days)
Fig. 4 - Compressive strengths for C40 concrete
0POZ:100PLC
10POZ:90PLC
20POZ:80PLC
30POZ:70PLC
40POZ:60PLC
50POZ:50PLC
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 16/29
1.Compressive strengths for all % replacements are
lower than those without replacement at early
ages(less than 28 days); and, with the exception of
C12 mixes, tend to be higher than mixes without
replacement at higher ages.
2. The property in (1) tends to increase with increase
in concrete grade.3.Maximum compressive strengths are obtainable, for
normal and high strength concrete mixes, for
pozzolana replacements of between 10 to 20%.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 17/29
Recommendations(i) Concretes
Concretes mixes designed to normal and high strength grades can made with Portland clay- pozzolana cement with an OPC/PLC replacement of between 10 – 20%.
Such concretes need to be cured with the best available means to obtain maximum results.
Clay- pozzolana cements are excellent when large concrete elements are to be cast, since gain of strength is low at early ages (because the cement- water reaction produces low heat ) and stresses due to rapid differential hardening will be minimal; reducing the likelihood of internal cracks.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 18/29
(ii) Sandcrete blocks Sandcrete blocks must have a minimum wetcompressive strength of 1.4 MPa at 28-days. In fact,most sandcrete blocks do not achieve this, yet theyseem to perform adequately because they are usedfor cladding ( the load being carried bybeams/columns or when laid flat, as load-bearingmasonry units).
A maximum replacement of 30% of OPC/PLC in the sand/cement mortar mix should satisfy this requirement .
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 19/29
(iii) Jointing
In masonry construction, the desired result is to havea weak bedding and transverse joints and stronger
blocks/bricks.
cracks will occur within joints rather than
through blockwork. joints can be caulked out and repaired, or when
‘pointed’ can conveniently hide cracks.
mortar of OPC/PLC and sand is considered too
harsh and traditionally a more ‘friable’ or ‘plastic’mortar has been preferred, and ‘masonry cement’or OPC and lime mix has been used.
A 30% pozzolana replaced cement behaves like masonry cement
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 20/29
(iv) Tiling, Screeding and PlasteringMortar for tile laying, wall plastering and floor screedingmust be as ‘plastic’ as possible (similar to jointing mortar).
A maximum of 30% OPC/PLC replacement by clay pozzolana is recommended for both tile laying and wall plastering.
Tiles must be soaked in water for at least 2hrs prior to laying, to prevent the absorption of the mortar
moisture by the dry tile, which will lead to the spalling- off of tiles. For screeding, the percentage replacement should be
a maximum of 20%, to offer higher resistance to abrasion by pedestrians.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 21/29
2. Durability Durability relates to how a structural element
appears and performs whilst in service. Poor
durability, whilst no imminently dangerous islikely to make users of a facility feeluncomfortable and unsafe and may prove costlyto maintain. It may eventually lead to a collapse
of the structure.
Durability may present itself in 4 ways.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 22/29
(i) Cracking
Cracking in cement and concrete may be from:
Shrinkage cracks (when mortar is prevented by formworkor other surfaces from moving when it is setting and by
the heat evolved during hydration). Excessive use of water in batching.
Rapid loss of water necessary for hydration.
Use of fine aggregate with too much silt and clay content
(max. should be less than 4%).The use of Portland clay-pozzolana cement will reduce
the heat of hydration and resist the sulphates and
chlorides in silts and clays.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 23/29
(ii) Sulphate and Chloride attack
Typical sources of sulphate and chloride solutions are:
- ground water of some clays;
- some sands;
-construction in saline environments (near sea or river);
- sub-soil construction;
-sewers, manholes, septic tanks and other harsh
environment; - construction in areas of high water table.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 24/29
These waters contain sodium, calcium or magnesium sulphates. The
sulphates react with both Ca(OH)2 (lime) and the hydrated C3A toform gypsum and ettringite, respectively.
Sulphate attack is shown by a whitish appearance, starting at theedges and corners, followed by cracking and spalling of concrete.This appearance is because sulphate attack results in the formation
of gypsum and ettringite , both products occupying a greater volume than the compounds which they replace so that expansion of hardened concrete takes place.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 25/29
Extent of sulphate attack depends on its concentrationand the permeability of the concrete (ease with whichsulphate can travel through the pore system).
If the concrete is very permeable:
water can percolate through its thickness andlime will be leached out.
evaporation at far face of concrete leaves behinddeposits of CaCO3 (formed by reaction of limewith CO2). This is known as efflorescence.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 26/29
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 27/29
Attack by sea water
- Though sea water contains sulphates andchlorides, the presence of the latter ensures that
sea-water attack is not generally accompanied bythe expansion of concrete. The is gypsum andettringite are more soluble in a chloride solution thanin water, which means that they can be more easily
leached out by the sea water.- Expansion may take place as aresult of the
pressure exerted by the crystallization of salts in thepores of the concrete.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 28/29
Crystalallization occurs above the high-water level,and it is by capillary action in the concrete. At thepoint of evaporation of water.
Prevention:
Use of Portland clay-pozzolana cement;
More importantly, by the use of concrete of low
permeability.
7/31/2019 Structural Use of Portland Clay-Pozzolana Cement
http://slidepdf.com/reader/full/structural-use-of-portland-clay-pozzolana-cement 29/29
3. Economy