10-The Effect of Pigment on Some Properties of Mortar for Brickwork by

ABSTRACT

Two laboratories examined the mech­anical properties of mortar with added pigment containing carbon black. One used a cement: lime : sand formulation whilst the other used a cement :sand: p/asticized mortar. The compressive, flexural and indirect tensile strength of mortar specimens were determined, and some compressive and shear tests carried out on brickwork specimens. The mortar containing lime undergoes a considerable decrease in compressive strength with increased pigment con­tent, whilst the plasticized mortar does noto

K. TROMAS

Brick Deve/opment Association, Londol/

M. G . COUTIE

University 01 Nottingham

and J. PATEMAN

S/l1Iderland Po/ytechnic

L' Effet du Pigment sur Certaines Propriétés du Mortier pour Maçonn­eries en Briques

Deux laboratoires ont examiné les propriétés de mortiers auxquels ont été ajoutés un pigment contenant du noir de carbone. L'un répondait à une composition ciment : chaux : sable, /' autre à une composition ciment : sab/e : mortier plastifié. Les résist­ances à la compression, à la flexion et indirecte à la lraction d'échanti/lons de morrier ont été déterminées. Le mortier contenant de la chaux subi! une diminution considérable de résist­ance à la compression quand la teneur en pigment augmente tandis que la résistance du mortier plastifié est inchangée.

Del' Einftufi eines Pigmentzusatzes auf einige Eigenschaften von Mortel for Ziegelmauerwerk

Zwei Laboratorien prüften die mechan­ischen Eigenschaften von M orteln mit kohlenstoffhaltigem Pigmentzus atz. Ein Mortel bestand aus Zement, Kalk und Sand, der andere war ein plastifizierter Zement! Sand-M ortel. Die Druck-, Biege- und indirekte Zugfestigkeit von M ortel-Probekorp­ern wurden bestimmt sowie einige Druck- und Scherversuche an Ziege/­mauerwerk ausgeführt. Mil steigen­dem Pigmentgehalt ver/ierl der kalk­haltige Mortel an Festigkeit , wahrend der plastifizierte Mortel keinen Fest­igkeitsverlust <.eigt.

1. INfRODUCTION Pigments, due to their non-cementitious character and relatively high surface area tend, if over prescribed, to reduce bond strength 1 and in some instances compressive strength. 2 Some authorities2 recommend that the amount of carbon black should be limited to 2- 3 % by weight of the cement. This paper reports the findings of two laboratories who studied the effect of additions to mortars of a pigment containing carbon black, iron oxide and an inert filler.

Hydrated lime to B.S.890S was used by Laboratory A and vinsol resin plasticizer- t pint/cwt of cement by Laboratory B.

2. EXPERIMENTAL

2.1 MateriaIs Used

Laboratory A used a 1:* :3 cement :lime:sand (by weight) mix for ali tests while Laboratory B used 1: 3, 1: 41 and 1: 6 (by weight) plasticized mortars. Both laboratories used ordinary Portland cement to B.S. 12 3

and a black pigment to B.S.1014 4 made up as follows:

Carbon black % 10

Black iron oxide 15

Granite dust filler plus lignosulphate plasticizer 75

The carbon black is 'Furnace Black', grease free, in the form of a soft dry powder consisting of amorphous free carbon with a low ash contento

Both laboratories added pigment as O, 2, 4, 6, 8 and 10 % of the cement by weight and in addition Laboratory B added 30 % and 50 % in some cases.

62

Laboratory A used Leighton Buzzard sand for mortar specimens and Sandiacres sand for some of the brick­work specimens while Laboratory B used Hargreaves sand. Sieve analyses are given in Table 1.

TABLE I - SIEVE ANALYSES DF SANDS USED

Percentage passing sieve

8.S. sieve Hargreaves size LeighlOn Sandiaeres

8uzzard Beginning End olproject olproject

3 . n;ln. 99-4 99·9 99 ·9 99 '8

7 96·6 99 ·8 99 ·7 99-6 14 87 ·6 99·7 98·0 98 ·6 25 61·8 98·8 89 ·7 93-2 52 10·8 27·8 46 ·2 38 ·8

100 1-4 10·2 15-4 11 '9 200 0 ·4 3·2 n.d n.d

At Laboratory A difficulties were experienced with the dropping-ball test for consistency so the water :cement ratio was fixed at 0·633 based on the practical experience of a bricklayer and several trial mortar mixes. At Lab­oratory B the water: cement ratio was calculated using wet sand in conjunction with the dropping-ball method. The moisture content of the sand was subsequently found to vary considerably and dried sand was then used .

K. Thomas, M. G. Coutie and J. Pateman 63

2.2 Mortar Tests

2.2.1 Laboratory A

The mortar was mechanically mixed and alI mortar cubes were made and cured in accordance with the draft standard.6 Six 4-in. cubes were made from each mix, three of which were tested at 7 days, two at 14 days and one at 28 days on a 300-tonf Denison machine. For compressive tests the loading rate was 672 lbf/in2/min, thus complying with the recommendation of SCAG.2

Three cylinders, 6-in. dia . x 12-in. long, were made from each mixo The steel moulds were filled in approxi­mately nine layers, each being tamped thirty times. The indirect tensile strength was determined after 14 days at a loading rate of 47·51bf/in2/min.

Flexural beams were made in four layers with ap­proximately 100 tamps per layer. These were tested in accordance with B.S.1881 7 with an effective span of 16 in.

2.2.2 Laboratory B

The mortar specimens were made in a similar way to Laboratory A. Six 4-in. cubes were made from each mixo Three were tested at 7 days and three at 28 days on a 200-tonf Denison machine, using a rate of loading of 2000 lbf/in2/min for the compressive specimens. Mor­tar cylinders, 4-in. dia. x 4-in. long, were cast in disposable cardboard moulds and the indirect tensile strength de­termined between i -in. thick x -t-in. wide plywood strips. 1 : 3 and 1'41 mixes were tested at 28 days and 1: 6 at 14 days.

2.3 Brickwork Tests

2.3 .1 Laboratory A

The bricks were three-hole perforated soft extruded Keuper Mar! wirecuts with a mean compressive strength of 86511bf/in2 and water absorption 24-h soak of 9·9 %. The range of values for twelve specimens in each case were respectively 7823- 9217Ibf/in2 and 9'1- 10'5 %.

Four crossed brick couplets were ma de from each mortar mix and cured under wet sacking protected from drying out by a polythene cover. The specially designed couplet testing apparatus (Figure I) consisted of two plates each with three projecting steel rods. The direct tensile strength was determined in a 5-tonf Leonard Farnell machine at a rate of 0·0727 in./min . One of each set was lost due to a sudden application of the top and bottom plates which although positioned as care­fullyas possible, caused enough shock load to break the bond.

Shear strength was determined on three bricks mortared together in which the central brick was displaced longi­tudinally by half a brick length. For the second series of these brickwork triplets the sand was changed to Sandi­acre. Four triplets were made for each mix cured in the same manner as the couplets. The triplets were initially tested in the Leonard Farnell machine but as the loads were found to be reasonably high the Denison machine was used at a loading rate of 270 lbf/min.

2.3 .2 Laboratory B

The bricks were three-hole perforated stiff extruded CoaI Measure Shale wirecuts with a mean compressive strength of 8356 Ibf/in2 and a range for nine bricks of 7350- 9000 Ibf/in2. Irregular and cracked bricks were

FIGURE I- Collplet testing apparatlls.

discarded before testing. The mean suction rate of six bricks was 7· 53 g/dm2/min, but the individual results were 5'58, 6,80, 7,33, 7,67, 8,40, 9·42 g/dm2/min.

The effect of brick suction on mortar strength was investigated by laying a mortar bed between two bricks, allowing it to remain for 1 min and then scraping it off into a 4-in. cube mould. The 7-day strength of these cubes is compared with similar ones 'without suction' in Table 11 for 0% and 50 % pigment using the 1:41 mixo The water :cement ratio was 1·3 and the consistence 10 ± 1 mm for the 'without suction' mortar, but these data are not known after suction.

Six 9-in. nominal (8i-in. actual) brickwork cubes were made for each increment of pigment in 1: 3 and 1 :4t mortars . The cubes were constructed, cured and tested in accordance with the Model Specification.2

Three were crushed at 7 days and three at 28 days on the 200-tonf Denison machine.

Shear strength was determined on three bricks mor­tared together with the central brick displaced longi­tudinally by one-quarter of the brick length, unlike Laboratory A. Curing was similar to the brickwork cubes . The 1: 3 mortar specimens were tested in the 200-tonf Denison machine and the 1: 4t mortar specimens in an Avery 50-tonfmachine.

3. RESULTS

3.1 Mortar Tests; Laboratory A

Table 2 gives the compressive strengths of mortar cubes at different proportions of pigmento The diminution in strength with increasing pigment content is c1ear!y seen at all curing times.

Cubes with 10 % pigment cured for 7 days had a mean compressive strength 34 % less than those without

64 The Effect of Pigment on Some Properties of Mortar for Brickwork TABLE 2- MEAN COMPRESS1VE STRENGTH OF I :t: 3 MORTAR (4-in.

CUBES) : LABORATORY A

Compressive strength (lbl/in 2)

Pigment 7 days 14 days 28 days (%)

Individual Mean Individual Mean Individual

2850 3510 O 2900 2840 3530 3520 3950

2770

2910 3270 2 2590 2743 3290 3280 3680 2730

2590 3040 4 2400 2463 3110 3075 3470 2400

2480 3070 6 2590 2420 2990 3230 2200 2910

2020 2540 8 2120 2073 2490 2515 2920 2080

1790 2380 10 1775 1878 2400 2390 2700 2070

pigment, while at 14 days and 28 days the decrease in strength was 32 %.

Table 3 gives the indirect tensile strength of mortar cylinders, and the transverse strength of bars.

The mean indirect tensile strength expressed as a percentage of the mean compressive strength of 4-in. cubes at 14 days varies between 9 A % and 12·6 % showing that the tensile strength does not diminish as rapidly with increasing pigment. lndeed, there is a linear decline of only about 8! % with increased pigment contento Transverse strength on the other hand falls by about 20 %.

T ABLE 3- I NDlRECT TENS1LE ANO TRANSVERSE STR ENGTH OF 1: t : 3 MORTAR TESTEO AT 14DAYS: L ABORATORY A

[

Indirect tensile strength Transverse strength (lbl/in 2) (lbl/in 2)

Pigment ( %) Percentages 01

Individual Mean mean equivalent Individual Mean cube strellgth

330 490 O 335 329 9·4 502 486

321 467

325 445 2 323 321 9·8 490 460

315 445

321 456 4 317 315 10·3 435 442

307 435

315 435 6 321 313 10'5 428 418

304 390

307 412 8 306 304 12·0 412 401

298 378

306 362 10 306 302 12·6 378 388

294 423 i

TABLE 4 - COMPREssrVE STRENGTHS OF 4-in . MORTAR C UBES AT 7 ANO 28 DAYS. LABORATORY B. WET SANO

Compressive strength (lbfl iIl 2)

Pigmellt 1:3 Morta/' 1:4-j-Mortar 1--------

1:6 Mortal' ( %)

,"dMd""' 1 M,., Individual Mean individual M ean

7 days 1160 805 I 560

O 955 1050 980 920 455 500 1035 980 i 490

2240 700 2 1925 2065 735 735

2030 770

2625 735 4 2310 2475 735 745

2485 770

2030 735 770 6 2590 2450 700 725 770 770

2730 735 770

1680 595 8 1715 1575 630 640

1330 700

1890 840 805 10 1820 1915 840 830 770 795

2030 805 805

28 days 1400 1225 770

O 1680 1585 1220 1210 825 775 1680 1190 730

2835 855 2 2940 2880 980 925

2870 940 ---

3290 1190 4 3535 3385 1190 1180

3325 1155

3710 1050 1010 6 4165 3815 1085 1110 1065 1040

3570 1190 1050

2555 1080 8 2555 2440 1150 1I10

2205 1105

3115 1080 1090 10 2940 3070 1105 1110 1010 1055

3150 1150 I

1065

3.2 Mortar Tests: Laboratory B

Table 4 gives the results of compressive strength tests on 4-in . mortar cubes made with wet sand. The water : cement ratio is not known for the 1: 3 mix but was 1·45 for the other two. The consistence of the 1: 6 mix is not known but was 10 ± 1 mm for the other two.

The 1: 3 mix shows the lowest strength with no pig­ment, and the highest at 4 % pigment for the 7-day cubes and 6 % pigment for the 28-day cubes. Because of the variability found with wet sand another set of tests was performed on mixes made with dried sand (Table 5). The water : cement ratio was O ·90 for the 1: 3 mix and 1·30 for the 1 :4l The 1: 3 mix with 30 % pigment was 0·95 and with 50 % pigment 1·00. The consistence was 10 ± 1 mm in both cases.

The variability of the 1: 3 mix using dried sand at 7 days, was less than for the undried sand specimens, but the average compressive strength over the O to 10 %

K. Thomas, M. G. Coutie and J. Pateman 65 TABLE 5- COMPRESSIVE STRENGTHS OF 4-in. MORTAR CUBES AT

7 DAYS. LABORATORY B. DRIED SAND

I Compressil1e slrenglh (lbf/in 2)

Pigment 1----- -- --------( %) I i : 3 Mortar J :4f Mortar

individual Mean individual Mean

1925 910 O 1785 1855 925 915

1855 910 -

1995 2 1995 1995

1995 -

1960 4 1925 1935

1925 -

1715 6 1680 1715

1750 -

1855 8 1820 1820

1785

1925 810 10 1855 1935 840 830

2030 840

1890 825 30 1925 1925 810 830

1960 855

1750 840 50 1820 1795 840 835

1820 825

pigment content range differed by only 2-!- %. No signifi­eant decline in strength oeeurred for this seeond mix with 30 % pigment eontent, but a fali in eompressive strength of 130 Ibf/in2 oeeurred between 30% and 50 %.

The 1: 4-!- mix mortar eubes showed close agreement at 7-day mean strengths for 0 % and 10 % pigment eontent giving values of 920 to 915 Ibf/in2 and 830 Ibf/in2 for both mortars for speeimens made from wet and dry sand respeetively. No fali in eompressive strength was re­eorded for speeimens eontaining 30 % and 50 % pigmento The 28-day wet sand speeimens had the highest eompres­sive strength at 0 % pigment, as for the 7-day speeimens, the lowest value oeeurring at 2 % pigment and then an exeeptionally eonstant strength up to 10 % pigment eontent.

The 1: 6 mix eubes were made only with undried sand and gave the minimum eompressive strength for 0 % pigment both for the 7-day and 28-day speeimens. Re­sults at 6 % and 10 % pigment eontent were uniform onee again for the two ages.

The indireet tensile strength of mortar eyIinders (Table 6), was minimal when pigment was omitted, and for eaeh individual mix the strength remained reasonably eonstant for pigment eontents between 2 % and 10 %. The water : eement ratio was 1·45 for ali mixes.

3.3 Brickwork Tests: Laboratory A There are no results for Leighton Buzzard sand without pigment beeause the first mortar mix was rejeeted as being too dry and there was insuffi.eient sand to repeat the mixo

The tensile strength of briek eouplets tested at 14 days (Table 7) shows no defini te trends.

T ABLE 6-INDIREc T TENSILE STRENGTHS OF DIFFERENT MORTAR MIXES TESTED AT Two AGEs. LABORATORY B

I indirect tensite strenglh at 28 days Indirect tensile

(lbf/in 2) strengrh ar I4 days (lbf/in 2)

Pigmenl 1:3 Mortar 1:4f Mortar 1:6 Mortar ( %)

Individual Mean Individual Mean Individual Mean

97 96 80 97 93 77 83 80

O 85 68 82 77 71

100

119 I 97 125 I 116 126

2 104 111 121 1 125

I 134 133

124 120 119 126 135

4 101 112 157 121 108 98

- - --- --127 127 112 119 130 128 118 110

6 120 115 127 105 105 120 102

119 123 112 129 125

8 134 118 127 91

119 130

1- -101 132 I 86 104 126 ' 130 101 95

10 128 111 127 93 117 109 109

I

TABLE 7- TENSILE STRENGTH OF 1:*:3 MORTAR AT 14 DAYS IN BRICK COUPLETS. LABORATORY A

Tensile strength Pigment (lbflin 2)

( %) individual Mean

2·2 2 2·3 6·3

14-3

78 ·1 4 66·3 53'6

16·5

11 ·6 6 28 ·1 19'1

17·7

12·7 8 18·0 13'9

11 ·1

50·5 10 57·0 47·0

31 ·2 49 ·1

66 The Effect of Pigment on Some Properties of Mortar for Brickwork

The shear tests on brick triplets were carried out at 14 days on Leighton Buzzard sand and 9 days with a second set using Sandiacres sand. The results are given in Table 8.

The results of the first batch are too variable to give a

TABLE 8-SHEAR STRENGTH OF BRICK TRIPLETS 1 :*:3 MORTAR. LABORATORY A

Shear strength (lbJ/in2)

Pigment Leighton Buzzard Sandiacre sand aI 9 ( %) sand at 14 days days

individual Mean individual Mean

108·9 O - - 119·6 114·9

108·1 123·0

66-4

I 116·4

2 132·5 96·2 118·2 114 ·5 83 ·5 114·7

102-4 I 108·6

193.6}

I 110·7

4 98 ·7 154 ·9 112·1 108·2 172 ·5 103·1 521·0 107·0

90 ·6 108·9 6 94 ·9 93·7 104·2 141 ·6

111·7 108·8 77-6 244-4

135 ·8 107-4 I 8 104·8 101·6 111·1 107 ·5 77 ·5 108 ·2 88 ·1 103·2

---107 ·6 112·9

10 70 ·1 91·0 107·9 128·3 95-4 J03·8

188-4

meaningful relationship with pigment content, but in the second batch if the very high values are ignored then there seems to be no effect due to pigmento

The initial brickwork triplet specimens gave some very high failure loads and, in some cases, the bearing surfaces of the bricks failed in compression prior to bond failure. In such cases it was noted that the surface of the brick in contact with the mortar bed sheared away from the remainder of the brick leaving the bond between mortar and brick undamaged. This apparently very high shear strength is diftlcult to explain fully, but it is likely that the optimum suction rate of the brick was achieved prior to laying in conjunction with well filled perforations, giving considerable mechanical assistance to the bond action. In each of these unusual specimens the perforations were in fact well-filled but the other parameters could not be checked to verify this theory.

3.4 Brickwork Tests: Laboratory B The compressive strengths of 9-in. brickwork cubes are given in Table 9. The consistence of all mortars was 10 ± 1 mm. The water: cement ratio of the 1:4} mortar was 1·45 ; that of the 1: 3 mortar is not known .

With the exception of 1:4} mortar at 7 days, the mixes with no pigment gave the lowest strengths.

The results of the tests on brick triplets are given in Table 10. The consistence of the mortar was 10 ± 1 mm in ali cases.

There is a slight increase in strength up to 10 % pig­ment but a considerable reduction in strength at the higher pigment contents. This seems to be due to the difficulty of mixing the water uniformly at these high proportions of pigment. During consistence tests the mixing had to be carried out by hand since the water does not combine with the pigment in the same way as it does with cement. Black globules of water were formed which had to be literally ground into the mix to combine with the available cement.

TABLE 9- COMPRESSIVE STRENGTH OF 9-in. BRICKWORK CUBES AT 7 AND 28 DAYS. LABORATORY B

Compressive slrenglh (lbJ/in 2)

Pigment 1:3 Mortar l:4f Mortar ( %)

I 7 days 28 days 7 days 28 days I

Individual Mean Individual Mean individual Mean individual Mean

2950 3560 3675 3465 O 3280 3040 3100 3485 3615 3405 3525 3365

2890 3800 2920 3105

4100 4730 3825 4520 2 3830 3960 5060 4470 3705 3685 3830 4175

3950 3620 3525 -

4010 3830 3J95

1

3580 3405

4 4100 4130 4940 4430 3500 4185 3865 4280 4520 4040 4010

4790 4520 3620 3765 6 5000 4895 4610 4350 3890 3690 4040 3810

- 3920 3560 3620

4730 4070 2680 3410 8 4130 4680 4700 5015 3830 3305 3560 3660

5180 5275 3410 4010

4970 3830 I 3345 3890 10 4070 4440 4J60 4190 1

3710 3445

1

3315 3700 4280 4580 3285 3890

K. Thomas, M. G. Coutie and J. Pateman 67

TABLE 10- SHEAR STRENGTH AT 7 DAYS OF BRICK TRIPLETS. LABORATORY B

1:3 Mortar I :4f Mortar

Pigment Shear strength Shear strength ( %) Water :cement (lbflin 2)

ratio Individual

93 O 0·9 96 I

72

89 lO 0·9 81

103

41 30 0·95 75

75

47 50 1·0 61

50

The effect of brick suction on mortar strength is shown in Table 11. There is about an 80 % increase in compressive strength of mortar subjected to suction, and the amount of pigment did not alter this effect, a1though the mortar with 50 % pigment had a strength approxi­mately 15 % higher for both the with-suction and without­suction specimens .

TABLE 11 - 7-DAY COMPRESSIVE STRENGTH (4-in. CUBES) OF MORTAR WITH ANO WITHOUT SUCTION

With suction Without suction

Pigment Weight Of l Compressive Weightof Compressive ( %) cube* strength cube* strength

(kg) (Ibf/in 2) (kg) (Ibf/in 2)

O 2·250 1505 2·175 870 O 2·240 1610 2·180 870

50 2·260 1820 2'190

I 1015

50 2·295 1890 2·185 1015

*1 kg = 2'2046 Ib.

4. CONCLUSIONS 1. The tests carried out at Laboratory A indicate that

there is a decrease in compressive strength of over 30 % when a pigment (containing carbon black) is added in proportions of up to 10 % to a 1: t : 3 cement: lime : sand mortar. The decline in strength was found to be ap­proximately linear with 2 % increments of pigment up to 10 % for each ofthe 7-, 14- and 28-day series of specimens tested.

2. Laboratory B tested 1: 3 cement : sand: plasticized mortar specimens and found generally that additions of the same pigment in small quantities (i.e. up to 4 or 6 %) tended to increase the compressive strength, possibly because the pigment acts as a filler when lime is not used .

3. Laboratory A found a slight linear decline in the indirect tensile strength of cement: lime : sand mortal' specimens with increasing pigment content and a more pronounced linear fall in strength for flexural specimens.

4. The plasticized mortar once again showed minimum strength for zero pigment content when measuring in-

Water: cement (Ibfl in 2)

ratio Mean Individual Mean

51 87 1 ·3 102 69

53

68 91 1·3 79 76

81

68 64 1·3 43 57

53

60 I

55 I

I \ ·3 65 57

52

direct tensile strength, but a reasonably constan t strength for pigment contents between 2% and 10 %.

5. The 9-in. brickwork cubes although producing rather variable results, do to some extent bear resemblance to the mortar strength in compression, the most notable aspect being that zero pigment content produced the lowest strength. Both mortar and brickwork cubes reached a maximum strength for the 1: 3 mortar at or near 6 % pigment content.

6. Brickwork couplets produced completely random results indicating no definite trends.

7. Brickwork triplets bonded with cement :lime :sand mortar generally showed a slight reduction in shear strength with increased pigment content, but results were not always consistent.

8. When brickwork triplets were bonded with the cement : sand : plasticized mortar, well-defined results were obtained, indicating that for an increase in pigment con­tent of up to 10 % a slight increase in strength occurs, but a considerable fall in shear strength takes place when the pigment content is increased to 30 % and 50 %.

9. The effect of brick suction on a cement: sand : plasticized mortar is quite dramatic. After contact for 1 min with bricks having a suction rate of 7 ·53 g/dm2/min an 80 % increase in the compressive strength of mortar cubes can be achieved both with and without pigment.

10. The introduction of certain pigments into mortar may well reduce the compressive strength of mortar cubes, but if as has been suggested elsewhere8 the mortar strength is approximately proportional to the 3y or 4y of the wall strength, the loss in strength of 1250 Ibf/in2 between the cubes containing no pigment and those containing 10 % would result in a loss of brickwork strength of the order of 6 Ibf/in2• The effect of brick strength is therefore of much greater s ignificance.

11 . It should be noted that at Laboratory B, the range of the results at a given maturity for individual mixes made with the wet sand is much greater than the range for a similar mix made with the dry sand, indicating that the moisture content of the sand was not constant during

68 The Effect of Pigment on Some Properties of Mortar for Brickwork the preparation of the mixo It is felt, however, that this does not detract from the validity of the interpretation of these results as expressed in the above conc1usions.

12. The compressive strength of mortar obtained by the two laboratories should not be compared directIy, since it is weIl known that the sand used by Laboratory A gives higher strengths than the sand used by Laboratory B.

ACKNOWLEDGEMENTS

The authors are indebted to Messrs. R. CruIley, D. Robson and J. N. Hornagold for carrying out the work upon which this paper is based.

Thanks are due to the University of Nottingham and SunderIand Polytechnic for providinglaboratory facilities. Also to Crossley Building Products Ltd. and Star Brick & Tile Co. Ltd. for the supply of bricks.

REFERENCES 1. THOMAS, K ., Bricks and Mortar. Consulting Engineer, July,

1968. 2. BRITISH CERAMIC RESEARCH ASSOCIATION, Model Specification for

Load-bearing Clay Brickwork. B. Ceram. R.A. Spec . Pub/. 56. 1967.

3. BRITISH STANDARDS INSTITUTION, Portland Cement (Ordinary and Rapid-hardening) B.S. 12: 1958.

4. BRITISH STANDARDS INSTITUTION, Pigments for Cement, Mag­nesium Oxychloride and Concrete. B.S . 1014 : 1961.

5. BRITISHSTANDARDS INSTITUTION, Building Limes. B.S. 890: 1966.

6. BRITISH STANDARDS INSTITUTION, Methods of Testing Mortars. Draft of B.S. 4551 :1970.

7. BRlTISH STANDARDS INSTITUTION, Methods of Testing Concrete. B.S. 1881 :1952.

8. KLEIN, A., Multi-storey Flat Buildings in Calcium Silicate Bricks and Blocks and the Testing of Wall Panels of Bricks, Blocks and Mortars for Calculated Masonry. 'Proceedings of International Symposium on Autoclaved Calcium Silicate Building Products' . London, Society of Chemical Industry, 1967. p. 239.