of the International Association of ENGINEERING GEOLOGY BULLETIN de l'Assocation internationale de GEOLOGIE DE L'INGENIEUR

E

No 30 PARIS 1984 t

G E O C H E M I C A L P R O P E R T I E S OF A G G R E G A T E S - C O N C R E T E Q U A L I T Y

P R O P R I E T E S G E O C H I M I Q U E S DES G R A N U L A T S - Q U A L I T E DES B E T O N S

RUESL~,TTEN Hakon G,* HOLM Jan Viggo**

Abstract

The mineralogical composition of Norwegian sand deposits influences the geochemical conditions and the rate of weathering. Chemical treatments of sand used for mortar aggregate testing (NaOH and citrate<tithionite-bicarbonate) extract various amounts of elements in the different soil profiles. A positive correlation is found within each quarry between relative mortar strength and the amount of K, Mg and Ca extracted from the sand samples. This correlation is even better when the amount of extracted K, Mg and Ca is adjusted for the water requirement index.

R~sum~

La composition mindralogique des gisements de sables norv6giens influence les conditions g6ochimiques et les vitesses de l'alt6ration. Des traitements c~miques (NaOH et citrate-dithionate-bicarbonate de Na) des sables & bdton montrent une extraction diff6- rente des 616ments suivant ia position des couches. Une relation e~ste pour chaque gisement entre la r~sistance du mortier et les quantit6s de K, Mg et Ca extraites des sables.

I n t r o d u c t i o n

The mortar strength for various mineral aggregates is discus- sed in the paper by Danielsen and Ruesl~tten [1] to this Symposium. Here, the in situ geochemical conditions of the sand deposits are discussed from the point of view of their mineralogical composition and their properties as aggregates in concrete.

Weathering processes

The major part of the fluvioglacial sediments in Norway were deposited at the end of the last glaciation, 12000 - 9500 years ago. During the later isostatic rebound of the Scandinavian platform the sediments were exposed to weathering by the ins of surface water. Mainly podzol prof'fles were developed by the interaction of che- mical weathering, biological processes and freezing-thawing.

Humic acids produced in the softs exhibit a great ability to chelate metal ions like iron, aluminium and manganese, and the organometal complexes migrate downards with the percolating water [2]. The metal complexes precipitate on the grain surfaces at different levels, and the staining of grains can be seen down to a depth of several metres.

Sodium, potassium, calcium and magnesium dissolved tend to follow the percolating water down to the groundwater. An exception is the calcite bearing deposits where preci- pitation of calcite on the grain surfaces takes place in the deeper parts (above the groundwater level).

* Department of Geology, University of Trondheim, The Norwe- gian Institute of Technology, Nonvay.

** NOTEBY, Norsk Teknisk Bygekontroll A/S (Partners of Norcon- sult A/S), Norway.

Weathering of sulphide minerals (mainly pyrite) in the de- posits is important in many areas. This process takes place above the groundwater level (where oxygen is available) and produces sulphuric acid and iron-compounds which cement the sand around the weathering site. The sulphuric acid attacks other minerals (such as calcite) and promote weathering reactions in the deeper parts of the fluvioglacial deposits.

Hence, there are two processes going on simultaneously :

- Weathering of rock fragments/minerals. - Precipitation on the grain surfaces.

In addition the weathering processes reduce the mechanical strength of the grains.

Fluvioglacial deposits investigated

Four fluvioglacial deposits were investigated :

Svelvik (Oslo-region), Dirdal and ,~rdal (Stavanger-region) and FIR (Trondheim-region).

The main differences between the deposits are their petro- graphical/mineralogical composition :

Svelvik consists of (in the gravel fraction) approximately 1/3 Permian intrusives, 1/3 Precambrian gneiss and 1/3 Cambro-Silurian sedimentary rocks (low grade metamor- phic) about half of which are calcite bearing. The sand fraction consists of approximately 90 % quartz and feldspar, while dark minerals and fragments of sedimentary rocks constitute the rest.

The petrographic composition of the ~rdal and Dirdal deposits are mainly Precambrian gneisses and granites. The sand fraction consists of 94 % quartz and feldspar, the rest is dark minerals and mica.

294

The F ~ deposit is derived mainly from Cambro-Silurian metamorphic sedimentary rocks : phyUites, conglomerates, sandstones (calcite bearing) and schists.

pH-measurements of sand samples from different levels in the quarries illustrate the differences in geochemical condi- tion especially the content of calcite (Fig. I). It is seen that fltrdal and Dirdal are acidic through the whole profile (inclu- ding the groundwater) while Fla and Svelvik give alkaline values in deeper parts of the deposits.

The chemical composition of the groundwater from the four localities also reflects the weathering conditions (Fig. 2). The content of calcium, bicarbonate and sulphate is highest in FI~ and Svelvik due to weathering of calcite and pyrite in the deposits.

Mortar t e s t i n g

Samples from the four localities were used as aggregates in a mortar testing programme where the following factors were kept constant :

- aggregate grading, - water : cement ratio (= 0.45), - aggregate : cement ratio (= 3.0), - relative density of mortar (i.e. void content).

A significant difference in mortar strength (after 90 days curing) was found depending on the sampling level in the quarries, (Fig. 3). This vertical variation cannot be explained by a variation in mineralogical composition only. Further- more, the vertical variations are different for the three regions investigated.

Chemical extractions

The relation between mortar strength and weathering conditions was investigated by chemical extractions of the sand aggregates :

- Extraction with 0.5 N NaOH at 80 ~ for 1/2 hr tosimu- late the etching by cement paste ;

- T h e r e a f t e r an extraction with Na-citrate-dithionite- bicarbonate (CDB) at 80 ~ to remove amorphous components not soluable in bases (3) ;

- The FI~ samples were treated with 0.5 N SrCI 2 to extract adsorbed sodium and thereby achieve a mea- sure for cation exchange capacity (CEC).

The NaOH-treatments extracted mainly Si, A1 and K (Fig. 4). As expected the amount of Si and A1 extracted increases towards the top softs, but a particular variation is seen near the groundwater level. Extracted K shows small variations only, but a decreasing tendency towards the top soil is seen, caused by weathering.

The CDB-extractions dissolved mainly Fe, A1, Mn, Ca, Mg and K, (Fig. 5). Fe, A1 and Mn are mainly extracted in the top soils and near the groundwater table (above). The amount of K, Mg and Ca extracted increases down through the profile towards the groundwater level. The cation exchange capacity (CEC) is illustrated by the FI] profile, which shows an increasing trend upwards (Fig. 5).

Mortar strength and e x t r a c t i o n s

The weathering removes cations from the mineral surfaces which lead to art increase of CEC. The water requirement for hydration of the mineral surfaces (i.e. hydration of adsorbed cations) also increases. Weathering also induces a mechanical weakening of the grains. While Fe, A1, Si and Mn is partly removed from the site of weathering no clear cut relation is found between mortar strength and the

amount of such ions extracted. The extracted K, Ca and Mg, however, correlate fairly well with mortar strength (Fig. 6). This positive correlation is even better when the water requirement index is taken into account (Fig. 7), even though the water requirement index alone shows no clear relation to mortar strength (Fig. 8).

The chemical treatment resulted in a general increase in mortar strength illustrated by the FI~ profile "treated" (Fig. 3). This is partly explained by abrasion of weak and brittle grains during the chemical treatments.

PROFILE (m)

k UA,k,

I

3 -

2- -

I-

_1--

-2--

Fig. 1 :

Fig. 2 :

~ ' - 0 ~

z-.O 50 60 70 80 i s ]

NX+',,. \\

?'%

o D o

I I I

2

~--pH

~H of

�9 Ol ~DAL o FL i

SVELVIK

m h.RDAL

Variations in pH of sand and groundwater in the four deposits.

mwqlt

~,00-

3.50 -

3.00-

2.50-

2,00-

HC0] ~ K

Na Cl

Mg SOl

Ca

1.5o-

I;00-

0.50- Oirdol

Ardal

Svelvik

"''"j~

FI6

. . . .

7/,/2Hml

~M: :it r

N:/i NL:

\ \ \ ~ . . .

|

pl-+

@

|

Chemical composition o f groundwater from the four localities.

2 9 5

~"L~ ~ ~o

- - C

SVELVlK FL~

70 80 8Q 710 8t0

J

f

AROAL

i

//

DJQDAL

~o ~,o 5~ ~o ~,o ~o

i I

ii

Fig. 3 : Variations in mortar strength (OR9 0) with sand aggxegate from the four locafities versus sampling level. The FI~ samples after chemical treatment are also shown.

PROFILE (m) 50

,I. ,L, (,~ I

1 + o

K~ao~

i'! 1

100 150 I I

m g d=ssotved in 0 . 5 N N a 0 H / k g a g g r e g a t e

200 250 300 I I I

/

�9 0IROAL

0 FL.& 4- SVE L'r

0 ~RDAL

Fig. 4 : Extractions of K, Si and AI with 0.5 N NaOH (mg dissolved per kg aggregate).

PROFILE

(m}

I

3= 2- I-

~ c

-I-

510 1010 150 200 ) t ~

4 ~ 0 ~ ~(K. Mg. C o l c o 8

- - -

I d t s s o l v e d in C D B / k g a g g r e g a t e [ mg

I 500 1000 t500 2000 2500 3000 i n i .L- , , Z,

@ 01ROAL

4- SVELVIK ; % 2 L K

§

C a t i o n e x c h a n g e

c a p a s i t y (meq / 1 0 0 0 g )

o 20 &o ' ' ' ' - -f

--2

Fig. 5 : Extractions of Fe, Si, AI, Mn, K, Mg and Ca with citrate- dithionite-bicarbonate (CDB), (rag dissolved per kg aggregate). Cation exchange capacity (CEC) of the FI~ samples is also given (meq. per kg aggregate).

296

NPa

60-

Fig. 6 :

(~R9Q

(MPo)

8 0 .

7 5 -

7 0 '

6 5

6 0

129.51

Fig. 7 :

e 01s 3 FLA

5VELVIK u A FRDAL

OP? / / op. ~

o [] /

/ / 2

. ~ ~ ~ " ~ T ~ A= / o ~ / / /

o o p ~ / / OP2 op~ /

/

oP, /

50 1oo 150 200 ElK Mg, Ca mg/1000g ~ggregote coa

Relative mortar strength (OR90) versus extracted K, Mg and Ca (by CDB).

FL,L DIRDAL /

X P 7 ARDAL / I / I /x .

I j / /

,.,~'.~ / I /

X P 3

3. /

+~7 I / I

l .Z@ / XPG

/ /

/ / i

t

I i PI

7 23 10)

/ /

SVELVIK . . / + / ' ~ 3 I

/ 3 4

/ + 3 . 3 /

/

6 0 ~ 80 t I 0 0 ~

{K, Mg. CO)NaOH~

K s

Relative mortar strength (oR90) versus extracted K, Mg and Ca (by NaOH + CDB) divided by the water require- ment index, K S .

O~R90

[MPo)

80-

7 5 -

70'

65.

60-

34+

X P 7

XP6

t-121

+31

--I-33

-~-32 130 0 1 ~

+36

O 1 2 X P 6

XP3 D22

+37

XP4

XPI

X P 2

I I I

3,0 3,5 L,0 K s

(o 1 (2951

Fig. 8 : Relative mortar strength (OR90) versus the water require- ment index, K S .

Conclusion

Fluvioglacial deposits in the three regions investigated show different geochemical conditions explained mainly by different mineralogical/petrographical composition.

The in situ weathering conditions of the sand used as aggre- gates influence .the mortar strength. The relative mortar strength is found to correlate positively with the amount of K, Mg and Ca extracted (by NaOH and CDB) from the sand samples ; especially when the water requirement is taken into account. This is explained by the surface conditions of the mineral grains. No clear correlation is found between mortar strength and Fe, A1, Si and Mn extracted.

References

o [1]DANIELSEN S.W. & RUESLATTEN H.G., (1984) :'"Feldspar

and Mica-Key minerals for f'me aggregate quality." Int. Syrup. on Aggregate, Nice, France.

[2]DIXON J.B. & "WEED S.B., (1977) : '~linerals in Soil Environ- ments." SoiI ScL Soc. of Am-, 948 p.

[3]MEHRA O.P. & JACKSON M.L., (1960) : "Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate." Clay and Clay Mineral 7: 317- 327.