A study of some Nigerian carbonate rocks for the building construction industry

ELSEVIER

Engineering Geology 37 (1994) 271 283

A study of some Nigerian carbonate rocks for the building construction industry E.O. Esu a, A.E. Edet a , S.C. Teme b, C.S. Okereke a Department of Geology, UniversiO' of Calabar, P.O. Box 1115, Calabar, Nigeria b Institute of Geosciences and Space, Technology Rivers State University qfScience and Technology, Port Harcourt, Nigeria ( Received July 1, 1992; revised version accepted March 31, 1994)

Abstract

A number of geotechnical analyses were carried out on selected carbonate rock samples from ten locations in Nigeria. This was to assess the suitability of these rocks as building construction aggregates. The analyses included uniaxial compressive strength, tensile strength porosity, water absorption and dynamic fragmentation. Evaluation of these carbonate rocks on the basis of a quality index (QI) scheme show that some lithofacies (i.e., calcareous siltstone, pisolitic limestone, marly limestone, massive limestone, sandy limestone, oncolitic limestone and fossiliferous limestone) which were obtained from AbinL Ashaka, Calabar-Ikom road, Ikot Okpora, Mfamosing and Nkalagu are the best for construction purposes. However, it is recommended that the susceptibility of each deposit to solution should be investigated.

1. Introduction

The success of building construction depends to a large extent on the availability of raw materials at affordable prices. Common raw materials generally used in the building industry include sands, gravels, clays and clay-derived products. Despite the widespread occurrence of carbonate rocks throughout Nigeria (Fig. 1), very little emphasis is placed on their direct use as raw material for building. The low premium placed on their direct application in the building sector may be explained in a number of ways. First, the lack of awareness of the potential uses of carbonate rocks in the building construction industry (beyond the production of asbestos, ceiling boards, roof sheets and portland cement) and second, the aesthetic applica*Author for correspondence. 0013-7952/94/$7.00 © 1994 Elsevier Science B.V. All rights reserved SSD1 0 0 1 3 - 7 9 5 2 ( 9 4 ) 0 0 0 1 1 - P

tion of carbonate rocks in the building construction depends mainly on their physical attributes which are more generally known within the confines of research laboratories and industries. In this paper, some physical and mechanical characteristics of some Nigerian carbonate rocks are evaluated for the suitability of these materials as building construction aggregates. In addition, this article presents some aspects of a proposed study of the geotechnical properties of Nigerian carbonate rocks. 2. Previous work

In the past some work has been carried out on the evaluation of Nigerian carbonate rocks for construction purposes. Most of these projects, however, were largely local projects. They included the geotechnical analyses of limestone specimens from southwestern and southeastern Nigeria by

I:" O. t::~'z~~'l a~ En~i,'lccrin,., (h,,,/ovr., ;7, /ou4, 27/ ?','3

272

1 \ ~ _ ~ f 77. 5 ~NIGE BENUE TROUGH

A

S

/

\

~

RI#'

l

(

.3

BASIN

CHaD

[ ~

Shale/Limestone and Sandstone k,~

")-.

A ANG

Voicanics

/' /~ /~ L L_L_-

A AB

I KA

Y ....

Yonder

Crys talline basemen

NK .... Nkalagu N G - . . Nobo AB- .Abini IK/~. 4kot 0kpam 0B . . . . 0botme ET . . . . Efankpini CK . . . . C a l a b a r Ikom road. N . . . . Mfomosing deposits used in present

NIGER

cK A'z~

I

_ ~Catbbar

D E LTA

9 km

study.

ro

/

F'ig. I. Locationsof carbonate rocks considered in this study, includingBenueTrough and Chad Basin ( At'ter Petters, 1982) Anifowose, (1984), Edet (1985), ldibie (1985), and Tame and Edet (1986), The first comprehensive work was performed by Tame (1991): however, the study was mainly executed to evaluate some Nigerian limestones as construction materials for highway pavement, and the different lithofacies within each deposit were not taken into consideration. 3. Study area

The three hundred and seventy five samples used m this study were obtained from Abini (AB),

Ashaka (AS), Mfamosing (M), Ngbo (NG), Nkalagu (NK), Yandev (Y), lkot Okpora ( I K A ) , k m 25 Calabar lkom road (CK) and Obotme (OB) (see Fig. 1). These localities cover two major sedimentary basins in Nigeria, the southern Chad Basin and the Benue Trough ( Fig. 1 ). Samples from the southern Chad Basin were collected in the Ashaka Cement Company Quarry. The deposits are composed of intercalations of calcareous sandstone, nodular marly limestone. massive limestone, calcareous hardground and gypsum layers of the Gongila Formation {Fig. 2

273

E. O. Esu et al./Engineering Geology 37 (1994) 271 283

I AGE

SE BENUE

TROUGH

SOUTHERN

QUATERNARY

CHAD BE

N IN

CHAD BASIN

FORMATION

IIIIll llllllII]l"}Illlll

II]:

PLIOCENE FOR

MATION

MIOCENE

KERRI

OLIGOCENE

FORMATION

KERRI

EOCENE

,.o s.ALE FORMATION

PALEOCENE MA A S T R I C H T I A N

~

S

U

K

K

~~'~,~.

~---._..22.~o~--~..~ CAMPANIAN

HIIIIlIIIIIIIIIIIIIIIIIII

A

_ ~

~___~_,,~N-

GOMBE

SANDSTONE

' itIllll tl

SANTONIAN CONIACIAN

FORMATION

TURONIAN

o izl C E1NOM A N I A N

.j-2A..~As,R,

]illlll LU

ALBIAN

:~ _~ o lz 3 (n

IIIIIIlll[lll[lllllllll

SANDSTONE

MFAMO~NG LIMESTONE AWl

PRE-ALBIAN

BIMA

FORMATION _._..

BASE

BASEMENT

t~ENT

Fig. 2. Stratigraphic succession of the study areas (After Petters, 1982).

The estimated thickness of the carbonate rocks at the Ashaka quarry is about 40 m. The sedimentary succession in the Benue Trough comprises a basal Neocanian-Albian sandstone discomformably overlain by the Albian Asu River Group (Fig. 2). The Asu River Group underlies the Cenomanian-Santonian Cross River Group. Post-Santonian deltaic sediments and coal measure sequences of about 2000 m thick rest uncomformably on the Cross River Group (see Fig. 2; Petters, 1982). The limestone occurrences at Yandev belong to the Gboko formation (Fig. 2). The sequence is

about 80 m thick and consists generally of two units; a lower limestone unit with a few thin beds of shale and an upper unit consisting of alternating marls and limestones. The different lithofacies units sampled for the present study include: Top Y-4: Y-3:

Light to dark grey sandy limestone; Grey massive limestones composed of pellitoids and sparry calcite; Y-2: Light grey marly limestone; and Bottom Y-l: Dark grey pisolitic limestone composed of carbonate mud and stylolites.

2"4

/:" (,'

IL~u cl . L Ew,,iswcrinc, UeoD,<..,r 3 7

l'hc Mfamosing Limestone is exposed in the Cross River limestone Quarry located about 35 km northeast of Calabar (Fig. 1). Tile limestone has all estimated thickness of about 30 m and displays about eight dil}'erent facies:

Top M, (Oncolotic limestone) Greyish. massive coarse-grained with 80 90'~, oncolites: M, (Fossiliferous limestone) Greyish. massive and line-grained, composed el' approximately 50", oncolites, pelletoids tllld Cal'bonate illLid. Shm~ impressions of pelecypods and moulds: M., (Stylolitic limestone) -Greyish. massive with stvlolites tit different horizons: fine- to mediumgrained and composed mainly of l'aecial pellets wilh \'cry few; oncolites and carbonatc i11t_ld. ~'la (Strnmalnlitie limestone) Greyish. nltissivo. composed of algal stromalolites and oncolitc. Pine/o \cry coarse-grtlilled with smaller frticlions made up of l'aocial pellets arid carboilate mud. r%'ls (Oneoliles limestone) Same as Ma but with stvloliie horizons tind without stronlatoliies. PineIo c.

l?04J 27l .',~.~

6l)". lntld (CK-1). Flus facies is tllltlcl-I~iiii ~.. , medium- to coarse-grained limestolw \\ ilh : i',il ec! amount of oncolitcs ICK-2) and ~t incdl~itl !~ coarse-grained limestone wilh a larger a~nl<,~! <,! oncoliles and pelleloids ( ( ' K - l ) Delta\ l h c ('ross Rivcr G r o u p comprises ~ {~,n>~rc>six e ('enomtiriain Santonian lithogenetic tlnit. !lie N ktllagu Fol'nlalion ( Petters and F~k;\,eozui Ic)$2 i. The locations of the limestone deposil~ ,,I ihc Nkalagu Formation are given in Table I ~111ctlie. ] Thc samples arc generally desert bed as I,>11,>\~• I:lt Abini, AB Dark grey. lhlc-graincd. ~c'i/ >erred. calcareous sandstone t b) lkot Okpora, IKA Dark gre> fos.~ilil'en>u~ limestone: (c) Ngbo, NG i\n upper dark grey. line-grained. well sorted sandy limestone ( N G - I ) a n d il Io\vcr grcyish, title-grained fossilil'erous linicslol/c t NG-2 t: Id ) Nkalagu, NK A lower glc5, lossilifcrou> limcslone and an upper light grey, shelly limestone xvitil intercalations of black calcareous shales \~ilh inoceranlus hnpression: and It) Obotme, OB An upper dark grey. biociasiic linlestone (OB I) and it lower dark grc>. ~allclt Iinlestonc with a l'cw (ossil illll-Uessions (()B2 I.

4. Method ofstudy ~\ Iotal of 375 carbonate rock samplc~ from dilTcrent deposits (Fig. 1. Table I) were sub.icctcd to index property :ind slrcngih characteiization Icsls. Phe index properties Ispccilic gravity, density. porosity ~ind water absorption) were carried otil in accordance with tile methods outlined bt Halllrol (1961 L F'rankiin (1970)and (ioodlllan

198O). {Jniaxial compressi\,e strength and Yotlng's lllodulus vttltlcS for the carbonate rocks \~,t21t" obtained according to the ASTM 2983-79 (I 9S(l) and ISRM ( 19791 standards. The size of the cylindrical specimens used for lhe test ranged from 23.58 54.45 toni in length and 15.70 16.70 mm in diameter. The strength results were corrected it, that o1" a standard size spechnen witll a diameter

275

E. O. Esu et al./Engineering Geology 37 (1994) 271 283 Table 1 Locations, designation and type of carbonate rocks under study S,,'N

Location(s)~

Age

Depth of sampling from surface (m)

Designation

Lithofacie(s):type of carbonate rock

1 2

Abini, AB Ashaka, AS

Turonian Turonian Cenomanion

10 40

AB AS-I

Mfamosing, M

Albian

Ngbo, NG

Turonian

Nkalagu, N K Yandev, Y

Turonian Albian

Etankpini, ET Ikot Okpora,IKA Calabar lkom road, CK

Albian Albian Albian

30 30 25 22 20 19 18 15 2 1 25 15 60 55 45 44 surface surface surface

Obotme, OB

Campanian Maastrichtian

AS-2 M-I M-2 M-3 M-4 M-5 M-6 M-7 M-8 NG NG-2 NK Y- 1 Y-2 Y-3 Y-4 ET IKA CK-1 CK-2 CK-3 OB-I

Calcareous sandstone Calcareous hardground ( Ferruginous limestone) Marly, limstone Oncolitic limestone Fossilifenus limestone Stylolitic limestone Stromatolitic limestone Oncolitic limestone Oolitic limestone Crustalline limestone Sandy limestone Fossiliferous limestone Calcareous siltone Fossiliferous limestone Pisolitic limestone Marly limestone Massive limestone Sandy limestone Oncolitic limestone Fossiliferous limestone Massive limestone Oncolitic limestone Oncolitic limestone Fossiliferous limestone

OB-2

Sandy limestone

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

surface

25 a See Fig. 1.

of 48 or 5 4 m m and a length-to-diameter ratio between 2 and 3 using the Turk and Dearman (1985) correction equation. 650

D °'is

am

1.754+0.535(D/L)

Where: 650: Uniaxial compressive strength of a 50 mm diameter rock; ~3m: Uniaxial compressive strength of a rock specimen having a different diameter; D: diameter of specimen; and L: length of specimen. Data on the dynamic fragmentation was obtained from the work of Teme ( 1991 ).

5. Results and discussion

5.1. Specific gravity, density, porosity and water absorption values" Using the data from Table 2, the mean specific gravity of the carbonate rocks range between 2.23 (the Ashaka calcareous hardground) and 2.76 (the oncolitic limestone at Calabar Ikom road (CK-2)). Most of the values are in the range of 2.40 to 2.61. Similarly, the mean dry densities (Table 2) do not show significant variations. The range of densities is between 2.37 Mg/m 3 for the Ikot Okpora fossiliferous limestone and 2.77 Mg/m 3 for the sandy limestone deposit at Yandev (Y-3). The variations in the specific weight are

E. D EM~ ~,I a/. [email protected], GeoloK' d7 , 1994) 27/ 2&'~

276

lablc 2 Mcan values of some physical properties of some Nigeria carbonate rocks S N location(st'

Lithofacies unit(s) b

Abini .\shaka

I

2 4 > (~ =

Mfamosing

Specilic gravity, (i

Density, 1'

POI'O.Sil }, Sl .

[)p, {lllg ill 3 }

Saturalcd ( illg in ~)

2.5~ 2.23

2.,',v 2.44

2.72 2.54

2.45 2.44

2.67 2.43

M-4 M-5 M-6 M-7 M-8 N(]-I NG-2 NK Y-I Y-2 ~-3 ",-4 t{l IKA ('K-I

2.50 2.2S 2.60 2.37 2.60 2.56 2.63 2.61 2.66 2.66 2.67 2.64 2.60 2.611 2.611

CK-2 ('K-3 OB- I OB-2

2.7~, 2d~l 2.61

AB AS-I AS-2 M-I M-2

.

.

.

.

.

7~;IIL ! .

.

.

.

.

.

.

;llnh~ )l'p{lOII

.

.\bsohllc

Elli:cti~c

('<,~

~"<,l

"~.$6

I /l

.',.69

I 12

.: ?,,: 24 4 5 " I

2.95 2 7I

12.71~

.; gtt

2.51) 2.29 2.65 2.39 2.52 2.50 2.63 2.69 2.~2 2.62 2."~ 2.-7 2.81 2.37 2.51

2.68 2.55 2.Sll 2 57 2.51 ~54 2 7~ 2,'4~ ~.66 2.63 2 77 2.95 2Nl) 7 5n " 4 "~

g.gg 14.111 5. 4 I

4 3,', ~ 15 2.95 "; 5g 2.~,3

4 n~

I l,'-; 4 If?

O.44 I 54 ~122 !~ 27 i ~,] O. I 7 1.711 tlS<~ 1 (I~

I 2:, 12;': ~ ~ II u.. It ,a It I 9' 2(Ja 1 :"

2.69 2.65 249

2 7~ ~S I 2.49 2.g4

401 2".4S

2 )7 !~', {146

4 c~l I ~< I 'i

i

M-3

x

9 Io II

Ngbo

12

I~ 14 I ~, 16 I~

Nkalagu Yandex

Ix

Fl'ankpini lkol O k p o r a ('alabar Ikom

I')

20 21

4 {12

I2.43 5.55 2.61 LTS

2<5 2.~0 260 IS4 ~.~=

", Iltl a 52 t~ f~'* ! s

I'l'qld

22 2~ 24 25

( )hot mc

~' Scc l i g I h Scc l'ablc 1

attributed to f a b r i c of the The

mean

differences carbonate

in a g e , l b s s i l c o n t e n t

and

rocks.

values of absolute

porosities

are pre-

in T a b l e 2, with the highest value of 1 4 . 0 1 % for the Mfamosing deposit (M-5, oncolitic limestone) and the lowest value (1.18%) from the lkot Okpora deposit. The effective porosities range between 0.17% and 4.38% for the Yandev deposits (sandy limestone, Y-4). The values of the absolute porosily generally exceed those of the effective porosity as expected. The difference between absolule and effective porosity presumably reflects both the proportion of occluded pores and tortuosity (Bell. 1981 ). sented

The

water

absorption

rocks range between Yandev)

and

Mfamosing).

6.6% A

of these

values

0.5'!4, ( p s o l i t i c

high

(oolitic water

carbonatc

limestone.

absorption

with

the

cement

lowers the durability

paste,

of the

on

one

aggregate

M-6,

generally

tends to increase the bounding between gate

Y-I,

limestone,

an aggre-

hand,

bul,

in a c o n c r e t e

on the other. 5.2. U n i a x i a / cO#nl)ressive ,wren£th, tensi/e xfrvn,kwh a m / Youn,~',v m o d u l u s values.

The mined

average was

uniaxial compressive

59.18

N / ' m n l 2. T h e

strength

highesl

deter-

value

of

E. O. Esu et aL/Engineering Geology 37 (1994) 271 283

130.31 N / r a m 2 was obtained from specimen CK-1 (Calabar-Ikom road) and the lowest (27.93 N/mm 1) belongs to an Obotme carbonate rock sample (OB-2 in Table3; and OB in Fig. 3). Specimens from all localities were saturated and subjected to unconfined compression tests. All samples showed a reduction in strength (Fig. 4), probably caused by the cementing material, which in this case is calcite. Other possible explanations include particle surface energy reduction (Rehbinder et al., 1967; Pugh, 1967), or an interparticle bond modification due to the existence of porewater pressure in poorly drained specimens (Attewell and Farmer, 1979). Evidence of the poor drainage of these specimens is reflected in the relatively high effective porosity values ( Table 2).

277

The Mfamosing limestone (M) with the highest values of porosity and water absorption (Table 2) showed the highest strength reduction (about 83%) and the lowest strength reduction (of 18%) in the specimens obtained from the Yandev deposits. This low value is consistent with the low porosity and water absorption values of the Yandev deposits presented in Table 2. Based on the Engineering classification of intact rock by Deere and Miller (1966), 83% of the specimens proved to be moderately strong (MS)-strong (S) while the remaining 17% are classified as very strong (VS) as shown in Fig. 5. The tensile strength values for the carbonate rock samples were obtained from the relationship given by Teme ( 1991 ) between tensile strength and uniaxial strength for Nigerian limestone. The rela-

Table 3 Mean uniaxial compressive strength and Young modulus values of the carbonate rocks used in this study S/N

Location(s)

Lithofacie(s) Uniaxial compressive strength units (N/ram 2) Dry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Abini Ashaka Mfamosing

Ngbo Nkalagu Yandev

Etankpini Ikot Okpora Calabar Ikom Road Obotme

AB AS l AS 2 M-1 M-2 M-3 M-4 M-5 M-6 M-7 M-8 NG-1 NG-2 NK Y-1 Y-2 Y-3 Y-4 ET IKA CK-1 CK-2 CK-3 OB-1 OB-2

Saturated

Tensile strength (N/mm 2) Dry

Young's modulus (GPa)

Coefficient of dynamic fragmentation (%) 19.54a 24.15 a

Saturated

46.82 74.67 35.85 37.58 25.16

22.10 36.90 33.60 12.90 19.46

3.84 5.97 4.86 3.00 2.01

1.77 2.95 4.64 1.03 1.56

2.36 12.56 4.61 4.61

22.22 15.68 73.39 32.97 44.18 42.53 68.93 58.84 105.60 60.94 37.85 116.78 62.12 35.24 130.31 103.56 55.48 38.05 27.93

5.79 5.72 49.57 24.21 36.03 31.51 43.64 46.12 96.00 22.75 33.50 27.05 28.32 31.87 46.83 33.55 31.07 24.99 19.34

1.82 1.25 5.87 2.64 3.53 3.40 5.51 4.71 8.45 4.88 3.03 9.34 5.00 2.82 10.42 8.28 4.43 3.04 1.36

0.46 0.46 3.97 1.94 2.88 2.52 3.48 3.70 7.70 1.82 2.68 2.16 2.27 2.55 2.30 2.68 2.48 2.00 1.52

2.26 0.80 8.76 6.11 4.35 5.56 20.50 15.30 23.15 4.53 8.52 16.45 3.89 3.45 45.00 53.20 24.78 13.27 7.62

" Average for each deposit (After Teme, 1991).

37.52a

21.42 19.14a 23.17 a

25.82 a 21.40 21.43

21.54

,k q~

c-i

OF

>-~

0 ~J

Z

o

I

o

I.wl

~n S ~ l ~ u a , . ~ l l

1

Luu~/NI

~I m

0 I

I

©

a^]~;~aJdua0 3

0 t

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i

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peu!ju0~ul7

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o

>'F

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l

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-I

~-o-~

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e^!~f~eJdwoa p0u!}uo0un

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~uJw/H 'n$ ~l~usJ~.~

-o

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G

E

ca

z

~o

L~

279

E. O. Esu et aL /Engineering Geology 37 (1994) 271-283

EwI

w

Islvsl

ES

ES ..... Estremely strong leo_

VS ..... Very strong S . . . . . . Strong MS ..... Moderately ~trong W . . . . . Weak EW ..... Extremely weak

G_)CK-3

E)ET

m

K-~

÷o

-

__~ I 0 -uJ "6

°"K \OOAS-2 ~

^@,

O Y-4

(90B - 2

IKA-SO M - 8 /

=?

/

/ I

/

.~u-I 0 Y-3 t ~ /

~\

-

I

e"°'2e.s-i/" ."

- .Q) O O B - I

G+

~M-5

I0 Unioxial

®M-?

I I O0

I000

compressive 3trength, M~a

Fig. 5. Engineering classification of some Nigerian carbonate rocks (Based Deere and Miller, 1966).

tionship is in the form of: 6tb = O.0826ult

where: 6tb: tensile strength of limestone specimens obtained from Brazilian test; and 6ult: uniaxial compression strength of rock specimens. The relationship according to Teme (1991) indicates that the tensile strength of the limestones is about 8.2% of the compressive strength, caused probably by the effect of deep weathering in the tropics (compared to about 10% in the temperate region rocks as observed by Hendron, 1978). The lowest tensile strength of 1.25 N/mm 2 was obtained for the Mfamosing limestone (M-5); while the highest value of 10.42 N/mm z was obtained for the specimens from the Calabar-lkom road (CK-1). Young's modulus ranges between 0.80 GPa

(M-5, Mfamosing limestone) and 53.20 GPa (CK-1, Calabar-Ikom road, see Table 2). Most carbonate rocks are classified as having a low to medium modulus ratio (Fig. 5). According to the scheme of Hendron (1978), most specimens tested proved to be elastic (Type I), plastic-elastic (Type II ) and plastic-elastic-plastic (Type IV ). Generally, most modulus values obtained are less than 20 GPa, thus indicating uniform deformation characteristics of the studied samples. In general, the uniaxial compressive strength of the carbonate rocks decrease with increasing porosity (Fig. 6). This is partly attributed to the fact that in any mechanically bounded aggregate (in this case mineral crystals), the overall magnitude of interlooking forces will depend on the total area of contact between individual particles. In the study area (humid tropical environment), the area of contact is expected to be greatly reduced, because of dissolution of the binding materials

280

A~ O. E~u el al. 'Engim,erit ,~ Geology 37

(

1994; 271 2~3

@CK-I

130

120

OY-4

110 -

Y-I

I00 90 80 NE E

70

z J=

QY-2 c ) E T

A$-2Q

60

(~CK-3

o

5O

M-b

\\~

eAB

40

\\

m

E o o

M-co

0 M'2

\

~) M- 5

~"-,, ,

30 20

08-2(9

\vaa-,

~.

~

",

".

I0

I

0

2

t \

l

N

6

4

P0rosity~

I 8

t I0

12

14

°/o

Fig. 6, Rehition between compressixc strength and porosil 5.

(calcite) by deep weathering. In addition, the values of the porosity and uniaxial compressive strength decrease and increase with age, respectively (Table 4). Decreasing porosity and increasing strength with age is expected, because the older

5.3. Durahi/it r

Because no special tests were carried out, the durability of the carbonates were assessed semiquantitatively using the strength, porosity and water absorption values.

Fable 4 Variation of some propel-ties with age

Age

Density ( N g m ~)

Porosity C,)

Strength ( N ram-')

Campanian Maastrichtian

2.49 2.94 2.40 2.45

3.48 3.53 3.42 3.53

19.34 24.99 27.93 48.16

Turonian

2.44 2.69 1.98 3.06

2.61 5.86 3.66 9.25

35.85 74.67 28.38 80.42

2.29 2.77 "':~'~ 2.84

1.84 14.01 0.88 10.77

15.68 130,31 30.59 130.31

Albian

the sediments, the longer the time for such processes as consolidation and cementation to operate.

6. E v a l u a t i o n o f the c a r b o n a t e r o c k as b u i l d i n g construction material

The evaluation of these carbonate rocks is based on lbur parameters, porosity, uniaxial compressix, c strength, tensile strength and dynamic fi'agmentation. Average dynamic fragmentation values for

E. O. Esu et aI./Engineering Geology37 (1994) 271-283

each deposit were obtained from Teme (1991) (Table 3). In addition to these four parameters (porosity, uniaxial comprehensive strength, tensile strength dynamic fragmentation), a fifth, water absorption is also used, because these rocks are being evaluated for possible use in the humid tropical climate of Nigeria. The method of evaluation involves three steps. The first is to assign weights to the parameters, the second step is to analyse the determined physical and mechanical parameters by assigning ratings and the final step is to compute a quality index using the weights and ratings. The quality index is then used to rate the potential use of the carbonate rocks as building construction materials.

6.1. Assigning weights On the basis of the relative importance of the physical and mechanical parameters as criteria for the quality of these carbonate rocks as construction aggregates, the parameters are classified qualitatively into five categories and are assigned weights (see Table 5). Uniaxial compressive strength with a weight of 5 is clearly the most significant parameter, and dynamic fragmentation with a weight of 1 is clearly the least significant.

6.2. Assigning ratings The five parameters (Table 5) are divided into different intervals and a rating is assigned to each interval as indicated in Table 6. The most significant interval has a rating of 5 and the least significant a rating of I.

Table 5 Weight assigned to various parameters Category

Parameter

Weight

1

Unconfined uniaxial compressive strength (qu) Tensile strength (T) Porosity (n) Water absorption (W) Dynamic fragmentation (D)

4 3 2 1

2 3 4 5

5

281

6.3. Quality Index, QI To evaluate a specimen, the quality index is computed by taking the sum of the product of weights and ratings of all the parameters, i.e.: QI= quwquR + TwTR + nwnR + Ww WR + DwDR

where subscripts W and R indicate the weights and rating for each parameter. On the basis of this equation, a general quality scheme is given in Table 7 and the carbonate rocks evaluated are shown in Table 8. Table 8 clearly shows that certain carbonate rocks in Nigeria can be utilized for building construction especially as aggregates. The carbonate rocks in this group include the calcareous siltstone (NG-2), pisolitic limestone ( Y- 1), marly limestone (Y-2), massive limestone (Y-3, CK-1 ), sandy limestone (Y-4, OB-2) oncolitic limestone (CK-2, CK-3) and fossiliferous limestone (NK). These rocks can, therefore, be quarried and used as aggregates for construction purposes. Other specimens with good potential as construction materials include calcareous siltstone (AB), calcareous hardground (AS-l), oolitic limestone (M-6), sandy limestone (M-8), fossiliferous limestone (IKA, OB-1, NG-1 ) (see Table 8). The carbonate samples NG-2, Y-1 Y-2, Y-3, Y-4 CK-1, CK-2, CK-3, Ob-1, Ob-2, AB, ASI, M-6, IKA possess medium to high strength, low to medium porosity, low to medium absorption and a medium to low coefficient of dynamic fragmentation. Carbonate rocks have two important properties: they are relatively soft and soluble in water. These two distinctive and important characteristics influence their engineering performance both as a rock material and a rockmass (Dearman, 1981). Therefore, under the humid tropical conditions especially in southern Nigeria, frequent contact of carbonates with water may have a deleterious effect on the durability and service record of buildings. However, because weathering due to solution can be prevented or at least minimized, such a defect should not be considered severe enough to avoid the use of carbonate rocks in the building industry.

282

E. O. Es'u et aL/'Engineering Geology 37 (1994) 271 283

Table 6 Ratings assigned to various ranges of the parameter Parameter

I

Unconfined uniaxial compressive strength qu (N/ram 2) 2 Tensile strength E/N/mm 2)

3 Porosity n (%) 4 Water absorption. 1l" (%) 5 Dynamic fragmentation, D (%)

Rating 1

2

3

4

5

<25 (very low)

25- 5(/ (low)

50 100 tmedium)

100 150 (high)

> 15o I ver? high )

<2.0 (very low) <20 (vmy hight >2 (very high) >40 (very high)

2.0 4.0 (low) 20-10 (high) 2 15 (high) 40-30 (high)

4.0 8.0 (medium) 10 5 (medium) 1.5 1 (medium 20 30 (medium)

8.0 12.0 (high) 5 15 i low) 1 0.5 (low) 2(} 10 (low)

:- IZo (very high) . 1.5 I very h m~ - 0.5 (veD h)a < 1~1 (very 1o,~)

Table 7 Quality assessment of carbonate rocks as building construction materials Class

Quality index value

Description as construction material

1 11 1II IV V

>40 31 40 21 30 I0 20 < 10

Very good Good Fair Poor Very poor

7. C o n c l u s i o n s

O n the basis o f the a s s e s s m e n t s c h e m e o f T a b l e 7, the c a r b o n a t e r o c k s at Y a n d e v , C a l a b a r - I k o m r o a d . O b o t m e , N k a l a g u (Class 1, T a b l e 8 ) a n d s o m e l i t h o - u n i t s at A b i n i , M f a m o s i n g a n d I k o t O k p o r a (Class II, T a b l e 8) are the best c h o i c e for construction purposes. These materials apart, from the high q u a l i t y i n d e x v a l u e s ( > 30), are c h a r a c t e r ised by h i g h u n i a x i a l c o m p r e s s i v e s t r e n g t h , l o w to m e d i u m p o r o s i t y , l o w to m e d i u m w a t e r a b s o r p t i o n capacity and low coefficient of dynamic fragmentation. T h e suitability o f these m a t e r i a l s c a n be f u r t h e r e m p h a s i z e d by the fact t h a t s o m e o f t h e s e c a r b o n ate r o c k s ( T u r o n i a n A b i n i ( A B ) a n d N g b o ( N G ) c a l c a r e o u s siltstone a n d s a n d s t o n e ) w e r e specifically q u a r r i e d f o r r o a d c o n s t r u c t i o n s . S o m e o t h e r s carbonates (the Turonian-Cenomanian Ashaka

Table 8 Quality indices for the different carbonate rocks Location

I 2 3 4 "~ 6 7 8 9 t0 II 12 13 14 15 16 17 18

19 20 21 22

23 24 25

Abini Ashaka

Lithofacies Quality index

AB AS- I AS-2 Mt'amosing M-I M-2 M-3 M-4 M-5 M-6 M-7 M-8 Ngbo NG-I NG-2 Nkalagu NK Yandev Y- l Y-2 Y-3 Y-4 Etankpini ET Ikot Okpora IKA Calabar CK-I lkom CK-2 CK-3 Obotme OB-I OB-2

" See Table 7.

Chtss l)escription'

33 45

11 1

Good Vel3 good

28 28

Ill Ill

Fan F~til

21 19 40 3O 31 34 48 49 59 50 41 59 42 38 57

IV IV 11 I11 I11 111

I)ooi Poor

49 48 37 35

II I I

I 11 1

Good Fair Good ( iood Very good Vcr~ good Vcr} good Ver3 good Vcr3 good Vcr} good Very good Good (h~,)d Very good Very good Good Very good

E. O. Esu et al./Engineering Geology 37 (1994) 271 283

calcareous hardground) are largely used as aggregates in concrete foundations within the vicinity of deposits. In addition, a major highway traverses the deposit at km 25 Calabar-Ikom road and no apparent evidence of pavement failure has been recorded in this section of road. Despite this service record, the susceptibility of each deposit to the effects of solution should be investigated.

Acknowledgements The authors are grateful to the authorities at Ashaka, Mfamosing, Nkalagu and Yandev quarries for permission to carry out field mapping and sampling within their premises. Financial support during the period of parts of this work in Tuebingen was received from the German Academic Exchange Service (DAAD), Bonn, to the second author and the University of Calabar.

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