FACTORS AFFECTING WORKABll..JTY AND BOARD LIFE OF CONVENTIONAL MASONRY MORTARS

J. T. Conwayl and J. M. Melander2

1. ABSTRACT

Workability and board life are recognized as being important characteristics of masonry monar in its plastic state as used by a mason. Relationships between these characteristics and other propenies of the field or laboratory mixed mortars, or of the cementitious materiais, are often assumed but not well established. In this

. investigation , twenty-one differenl mortars were evalualed under hot-weather, simulated job-site construction conditions. In addition to evaluation of workability by an experienced mason - board !ife, water content, and air content measurements were recorded for each mortar. Laboratory tests to determine air content, water retention, and compressive strength were conducted on mortars prepared using each of the cementitious materiais. Setling time and early stiffening lests were run according to ASTM slandard methods of testing for hydrau!ic cements. Fineness tests and particle size distributions were also determined for each of lhe different cementitious materiais. Relationships between these variables are examined in this paper. Regression analysis of the dala from this study indicates that a slrong relationship exists between some of the variables measured and workabi!iIY or board !ife, while little or no relationship is evident for other variables.

2. INTRODUCTION

Successful masonry construction is very much dependent on lhe skill of lhe craftsman in using mortar and units to build masonry assemblies. Masons understand the imponance of those plastic properties of monar which enable them to accomplish their tasks. They term these characteristics as the "workability" of the mortar - their evaluation of how the mortar adheres to or slides from a trowel , spreads on the masonry unit, clings to vertical surfaces, extrudes from joints wilhout dropping or smearing, and accommodates positioning of the unil withoul subsequent shifting due to

KEYWORDS: Masonry; Monar; Workability; Boardlife.

1 Manager Quality Assurance, Research and Development , Holnam, Inc. , Dundee, Michigan , 48131, USA.

2Masonry Specialist, Engineering Services. Codes & Slandards, Ponland Cement Association , 5420 Old Orchard Rd. , Skokie. Ill inois. 60077 , LSA.

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its weight or the weight of successive courses. The term, "board life," is commonly used to indicate how long the mortar retains it's "workability."

Evaluation of these characteristics remains somewhat subjective, although numerous laboratory and field test procedures have been proposed to measure specific properties of mortars related to workability and board life. Some of these procedures have been adopted as part of current materiais standards. ASTM C270, the Standard Specification for Mortar for Unit Masonry, and ASTM C91, the Standard Specification for Masonry Cement, both include water retention requirements for mortar. Early studies indicate that the water retention test (currently defined in ASTM C91) was developed to quantify the ability of a mortar to retain its flow under conditions felt to simulate placement of mortar on porous units [Palmer, 1932) . Setting time limits for mortar were also suggested in the initial discussion of development of a mortar standard based on reasoning that mortar should have setting properties which would perrnit sufficient time for the work to be done properly and which would likewise permit consrruction to progress rapidly [ASTM, 1938). These proposed criteria for a minimum and maximum setting time were later deleted from draft mortar specifications. However, set time lirnits were incorporated into ASTM C91 and are currently part of that specification.

Additional workability related tests such as the ASTM C451 , Method for Early Stiffening of Ponland Cement (Paste Method), are sometimes modified and adapted for use as quality control tests for cements , including masonry cements. More recently field evaluation tests including the cone penetrometer and the modified concrete penetrometer test [Conway, 1980) have been adopted as part of ASTM C780, the Standard Method for Preconstruction and Construction Evaluation of Mortars.

Previous studies investigating relationships between measured properties of monars have included consideration of some of the variables incorporated in this study. However, the focus of past investigations has been primarily in evaluating the effect of these variables on properties of the hardened mortar or on properties of masonry assemblies [Huizer eLal, 1974) [Huizer, 1976). The focus of this investigation was to develop a quantitative assessment of workability and board life for twenty-one masonry mortars and compare those "ratings" to other measured parameters of the mortars and cementitious materiais. The cementitious materiaIs used in this study were packaged products designed to be mixed with sand and water. They included conventional masonry cements, colored masonry cements, and cementllime blends.

3. TEST PROCEDURES

The investigation included evaluation of the mortars mixed under conditions similar to those encountered at a construction site in hot weather as well as laboratory testing of mortar materiaIs.

3.1 Field Test Procedures

The field testS were conducted in Holly Hill , South Carolina, during August of 1993. Ambient temperatures ranged from 32 to 43 degrees C. Two experienced masons were employed to evaluate the workability characteristics of different mortars. The actual mixing of the field monars was performed inside a laboratory using a conventional one bag mortar mixer. Mortar was then taken in wheel barrows outside of the laboratory for sampling and testing under what are considered typical construction conditions during hot-weather construction in the Southeastem United States. The volume ratio of sand to cementitious materiaIs was maintained at 3 to 1 for ali mortars. A local masonry sand having gradation as indicated in Table 1 was used in ali "field mixed" mortars. One of the masons assisted in the mixing of the monar to establish workable consistency, however, neither of the masons evaluating the mortars knew what specific ingredients or brands of materiais were contained in the different monars.

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The initial consistency of each field Table 1--Masonry Sand Gradation mixed mortar was evaluated using a _---,;.,--______ ----""-,,,_-,.------modified concrete penetrometer as Sieve % Passing described in Annex A3 of ASTM Size Actual ASTM CI44 Limits C780. A scale reading of 50 using the ---,2:-. ~36.,;.:.:-mm--~1.:,.;0-i0'-';. 0----'-.;:.:....~95~to-71O~0~~ modified concrete penetrometer was 1.18 mm 98.5 70 to 100 established as the target value for that 600 llm 72.5 40 to 75 initial consistency. After a three 300!lm 30.6 10 to 35 minute mix time, the consistency of the 150!lm 6.3 2 to 15 mortar was checked in the mixer. lf 75!lm 0.5 that consistency in the mixer was 50 ± _---'-..:........c..:.;-'-'-__ ..:......:....-________ _

10, the batch of mortar was clischarged into a wheel barrow and taken to the work site. There, a sample of the mortar was placed on a damped plywood mortar board and a specimen was prepared for measurement of initial consistency. Subsequent consistency reaclings were taken at 30 minute intervals until a scale reading of 200 or more was observed using the modified concrete penetrometer. Mortars were remixed by hand after each penetration reading , but no additional water was added to any of the mortars.

Additional parameters recorded for field mixed mortars included the time of day that mixing was completed, ambient temperatures, the amount of water added to each batch, the air content, the workability rating , and a log of observations. Air content of field mixed mortar was determined using the pressure meter method described in ASTM C780, Annex A6. The masons determined the workability rating of each mix by assigning each mi x a number from I to 4 (l-excellent , 2-good , 3-fair, 4-poor). This rating was a subjecrive overall assessment made after working with a monar.

3.2 Laboratory Test Procedures

Laboratory tests were conducted on samples of the cementitious materiais used to produce the field mixed mortars. Tests included evaluation of laboratory mixed mortar properties using procedures required by ASTM C91 , evaluation of properties of laboratory mixed cement pastes, and physical and chemical tests of the cementitious materiais. Table 2 lists the laboratory determined parameters and the appropriate reference ASTM standard(s) defining the test procedure used.

Table 2--Laboratory Test Procedures

Test Flow Water Retention Air Content Compressive Strength Normal Consistency Vicat Time of Set Gillmore Time of Set Early Stiffening Autoclave Expansion Fineness by 45-um (No. 325) Sieve Fineness by Air Permeability (Blaine) Percent less than 2-micron Percent MgO Percent S03 Loss on Ignition Insoluble Residue

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Procedure ASTMC109 ASTM C91 ASTM C91 , ASTM C185 ASTM C91, ASTM C 109 ASTM C187 ASTMC191 ASTM C206 ASTM C451 ASTM C91, ASTM CI51 ASTM C430 ASTM C204 Coulter Panicle Size Analyzer ASTM C1l4 ASTM Cl14 ASTM Cll4 ASTM Cl14

4. RESULTS

Data from the field mixed mortars are summarized in Table 3. Values for the board !ife determination were obtained by plotting the modified concrete penetrometer readings tak:en at 30 minute intervals and determining the elapsed time required to reach a scale reading of 200. Fig. 1 illustrates how board life and normalized board !ife values were determined from modified concrete penetrometer readings for mortar Sample 1.

Sample Type No.

1 N 2 S 3 S 4 N 5 S 6 N 7 SIM 8 S 9 S 10 N 11 N 12 N 13 S 14 S 15 S 16 N 17 M 18 N 19 N 20 N 21 S

Avg. Std. Dev.

(/) 250 , gf 200

'Õ 150 :e

~ 100

50

O

Min. Max

N

•

O

Table 3--Data: Field Mixed Mortars

Workability Board Air Water Initial Rating Life Contem Content Penetration

(ITÚn) (% ) (L) Reading 87 14.6 28.4 60 79 14.0 28 .8 55

2 64 12.9 29.1 50 2 44 14.4 31.4 90 4 30 14.2 28.8 80 I 83 14.8 29.1 45 1 74 13.8 28.0 50 4 41 10.7 27 .3 90 1 53 12. 1 32.2 50 1 60 13.3 30.7 20 1 73 16.4 28.8 60 4 5 3.7 36.7 100 4 16 5. 1 33.7 95 1 60 12.7 36.0 20 1 60 15.3 26.1 60 2 43 12.6 29.5 40 2 56 11.8 26.5 70 I 39 15.7 27.3 50 2 45 10.3 31.8 100 1 60 15.6 26.9 50 1 50 14.6 28.8 70 1.8 53 12.8 29.8 62 1.2 21 3.2 2.9 24 I 5 3.7 26. 1 20 4 87 16.4 36.7 100

21 21 21 21 21

Board Life = 87 minutes

r"I ~ .. I-~

~

f-.-•

20 40 60 80 100

Time - Minutes Fig. 1 Penetrometer Scale Reading as a Function of Elapsed Time for Mortar

Sample 1.

Note that although the initial consistency of the mortars was targeted for a scale reading of 50, several of the samples exhibited initial modified concrete penetrometer readings well over 60. These represent samples exhibiting significant stiffening between the

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time that the consistency was checked in the mixer and when the initial consistency determination was made at the work site. The initial consistency of Samp1e 10 was mixed to a significantly wetter consistency than others, as indicated by the initial modified concrete penetrometer reading of 20. The water requirement for that mortar was misjudged during mixing.

Data obtained from laboratory tests of the cementitious materials used in the field mixed mortars are summarized in Tables 4, 5, and 6.

Table 4--Test Results on Laboratory Mixed Mortars

Air Water Flow Mixing Compressive Strength Content Retention (%) Water (MPa)

(%) (%) (rnl) 2Day 7 Day 28Day Avg. 16 85.4 110 205 9.0 13.5 16.8

Std. Dev. 4 5.5 3 16 5.2 6.6 8.0 Min. 5 71.5 105 186 2 .6 4.5 6.6 Max 21 94.3 115 244 23.8 3l.6 38 .5

N 21 21 21 21 21 21 21

Table 5--Test Results on Laboratory Mixed Cement Pastes

Normal False Setting Time (min) Autoclave Consistency Set Vicat Gillmore Expansion

(%) (%) Initial Final Initial Final (%) Avg. 26.4 47.4 175 309 213 354 0.033

Std. Dev. 2.6 26.5 83 93 64 76 0.027 Min. 22.3 6.1 60 170 110 270 -0.008 Max 30.6 86.8 420 590 350 590 0.119

N 21 21 21 21 21 21 21

Table 6--Laboratory Tests of Cements

Fineness ComI1osition < 2 ~ < 45 ~ Blaine MgO SÜ) Loss on Insoluble

(%) (%) cm2/g Ignition Residue Avg. 24.2 93.9 7400 2.26 l.50 16.61 3.40

Std. Dev. 4 .7 3.7 910 1.53 0 .31 5.17 2.87 Min. 15.7 82.3 6000 1.13 0.72 4.87 0 .28 Max 32.4 99.2 9280 6.88 2.17 23.53 10.91

N 21 21 21 21 21 21 21

5. ANALYSIS

A correlation matrix for the measured variables is shown in Table 7. Entries in that table that are above the identity diagonal are values for the coefficient of correlation, r. Entries below the identity diagonal are values for the square of the coefficient of corre1ation, r2. Negative values of r indicate that the modellinear equation describing the relationship between the two variables has a negative slope.

Relative values for coefficients of correlation, obtained by pairing various parameters with workability are shown in Fig. 2 . Similar information is shown for analysis performed using board tife as the dependent variable in Fig. 3.

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-" w

'" o

Table 7--Correlation Matrix

Variable I 2 3 4 5 6 7 8 9 In 11 12 13 1 Workability Rating 1.000 -0.782* -0.723 0.310 0.707 -0.766 -0.589 -0.284 0.609 0.453 0.388 0.381 0.671 2 Board Life 0.611 1.000 0.715 -0.475 -0.595 0.722 0.488 0.390 -0.751 -0.374 -0.274 -0.274 -0.717 3 Air Content (Field) 0.523 0.511 1.000 -0.677 -0.542 0.911 0.669 0.161 -0.759 -0.620 -0.520 -0.502 -0.605 4 Water Content (Field) 0.096 0.225 0.458 1.000 0.143 -0.588 -0.111 -0.153 0.808 0.322 0.179 0.141 0.678 5 Initial Penetration Reading 0.500 0.354 0.293 0.020 1.000 -0.580 -0.448 -0.379 0.560 0.152 0.104 0.106 0.518 6 Air Content (Lab) 0.587 0.521 0.829 0.345 0.336 1.000 0.659 0.343 -0.693 -0.620 -0.540 -0.534 -0.639 7 Water Retention 0.347 0.238 0.448 0.012 0.201 0.435 1.000 0.097 -0.275 -0.577 -0.609 -0.578 -0.338 8 Flow 0.081 0.152 0.026 0.023 0.143 0.118 0.009 1.000 -0.219 0.159 0.170 0.159 -0.198 9 Water Content (Lab) 0.371 0.564 0.576 0.654 0.313 0.481 0.076 0.048 1.000 0.376 0.207 0.177 0.885 10 Comp. Strength (2 Day) 0.205 0.140 0.384 0.104 0.023 0.385 0.333 0.025 0.142 1.000 0.975 0.967 0.322 II Comp. Strength (7 Day) 0.151 0.075 0.271 0.032 0.011 0.291 0.371 0.029 0.043 0.951 1.000 0.991 0.187 12 Comp. Strength (28 Day) 0.145 0.075 0.252 0.020 0.011 0.286 0.334 0.025 0.031 0.935 0.983 1.000 0.133 13 Normal Consistency 0.452 0.5130.366 0.460 0.2680.4090.114 0.039 0.784 0.104 0.035 0.018 l.OOO 14 False Set 0.040 0.078 0.060 0.220 0.063 0.066 0.003 0.080 0.324 0.013 0.056 0.095 0.431 15 Set Time (Initial Vicat) 0.097 0.009 0.210 0.292 0.075 0.187 0.000 0.002 0.221 0.032 0.015 0.012 0.141 16 Set Time (Final Vicat) 0.171 0.020 0.226 0.277 0.122 0.251 0.002 0.005 0.255 0.075 0.047 0.038 0.206 17 Autoclave Expansion 0.013 0.005 0.007 0.093 0.016 0.001 0.032 0.027 0.071 0.207 0.265 0.274 0.036 18 Set Time (lnitial Gil.) 0.173 0.0850.322 0.456 0.1140.2930.0130.020 0.4650.060 0.0230.0130.376 19 Set Time (Final Gil.) 0.166 0.029 0.225 0.325 0.065 0.241 0.004 0.007 0.249 0.064 0.039 0.030 0.235 20 Fineness (-211m) 0.102 0.100 0.512 0.343 0.001 0.304 0.256 0.089 0.197 0.450 0.391 0.312 0.142 21 Fineness (-45 11m) 0.123 0.1350.011 0.010 0.028 0.035 0.178 0.045 0.014 0.134 0.171 0.136 0.161 22 Fineness Blaine 0.015 0.018 0.097 0.001 0.021 0.078 0.172 0.077 0.004 0.367 0.382 0.326 0.013 23 MgO Content 0.055 0.077 0.319 0.483 0.002 0.195 0.000 0.020 0.276 0.074 0.026 0.014 0.148 24 S03 Content 0.003 0.000 0.076 0.377 0.038 0.077 0.044 0.005 0.094 0.020 0.056 0.066 0.069 25 Loss on Ignition 0.065 0.033 0.225 0.245 0.004 0.139 0.112 0.079 0.130 0.428 0.433 0.352 0.134 26 Insoluble Residue 0.169 0.103 0.197 0.053 0.012 0.080 0.194 0.165 0.077 0.276 0.268 0.220 0.087 *Entries above the identity diagonal are values for Coefficient of Correlation r. Entries below the identity diagonal are values for r2.

W 0'\

Variable I Workability Rating 2 Board Life 3 Air Content (Field) 4 Water Content (Field) 5 Initial Penetration Reading 6 Air Content (Lab) 7 Water Retention 8 Flow 9 Water Content (Lab) 10 Comp. Strength (2 Day) 11 Comp. Strength (7 Day) 12 Comp. Strength (28 Day) 13 Normal Consistency 14 False Set 15 Set Time (Initial Vicat) 16 Set Time (Final Vicat) 17 AlIlOclave Expansion 18 Se! Time (Ini!ial Gil.) 19 Se! Time (Final Gil.) 20 Fineness (-2 ~m) 21 Fineness « -45 ~m) 22 Fineness Blaine 23 MgO Content 24 S03 Content 25 Loss on Ignilion 261nsolllble Residlle

Table 7(cont)--Correlation Matrix

14 15 16 17 18 19 20 21 22 23 24 2S----zQ 0.200* -0.312 -0.413 -0.113 -0.416 --=U.401 ~O.319 00351 -O.12T 0.234 0.053 -0.255 --=U.411 -0.280 0.094 0.141 -0.071 0.291 0.171 0.316 -0.368 0.134 -0.277 0.014 0.183 0.321 -0.246 0.458 0.476 -0.083 0.568 0.474 0.716 -0.104 0.311 -0.564 0.275 0.475 0.443 0.470 -0.541 -0.526 0.305 -0.675 -0.570 -0.586 -0.102 -0.039 0.695 -0.614 -0.495 -0.230 0.252 -0.274 -0.349 0.126 -0.338 -0.255 -0.033 0.166 0.146 0.041 0.194 -0.059 -0.111

-0.257 0.432 0.501 0.029 0.541 0.491 0.551 -0.188 0.279 -0.441 0.277 0.373 0.284 -0.054 0.002 0.043 0.180 0.114 0.061 0.506 -0.422 0.415 -0.021 -0.209 0.335 0.441 -0.283 0.048 0.073 -0.164 0.141 0.081 -0.298 0.213 -0.278 0.142 -0.068 -0.281 -0.407 0.569 -0.470 -0.504 0.266 -0.682 -0.499 -0.444 0.119 -0.065 0.525 -0.307 -0.361 -0.278

-0.115 -0.179 -0.273 -0.455 -0.245 -0.253 -0.671 0.367 -0.606 0.271 0.141 -0.654 -0.526 -0.237 -0.123 -0.218 -0.515 -0.152 -0.19R -0.625 0.414 -0.618 0.162 0.237 -O.65R -0.51 R -0.308 -0.109 -0.194 -0.524 -0.114 -0.172 -0.558 0.369 -0.571 O.IIR 0.258 -0.593 -0.469 0.656 -0.375 -0.454 0.191 -0.613 -0.485 -0.377 0.40 I -0.112 0.385 -0.264 -0.365 -0.295 1.000 -0.075 -0.127 0.399 -0.310 -0.163 -0.182 0.144 -0.071 0.399 -0.301 -0.012 0.017 0.006 1.000 0.957 -0.261 0.930 0.932 0.301 0.229 -0.070 -0360 0.523 0.472 -0.027 0.016 0.916 1.000 -0.100 0.912 0.932 0.334 0.088 0.019 -0.410 0.461 0.526 0.075 0. 159 0.068 0.0 I O 1.000 -0.313 -0.235 O.(l97 -0.198 0.268 0.221 -0.291 0.074 0.176 0.096 0.864 0.831 0.098 1.000 0.914 0.396 0.115 0.031 -0.436 0.500 0.519 0.099 0.027 0.868 0.869 0.055 0.836 1.000 0.347 0.048 0.091 -0.398 0.454 0.530 0.134 0.033 0.091 0.111 0.009 0.157 0.120 1.000 -0.278 0.668 -0.706 0.326 0.755 0.682 0.021 0.053 0.008 0.039 0.013 0.002 0.077 1.000 -0.557 0.016 0.289 -0.336 -0.515 0.005 0.005 0.000 0.072 0.001 0.008 0.446 0.310 1.000 -0.328 -0.067 0.430 0.583 0.159 0.130 0.168 0.049 0.190 0.158 0.499 0.000 0.107 1.000 -0.614 -0.495 -0.459 0.091 0.274 0.213 0.085 0.250 0.206 0.106 0.084 0.005 0.377 1.000 0.126 -0.161 0.000 0.222 0.276 0.005 0.269 0.281 0.570 0.113 0.185 0.245 0.016 1.000 0.547 0.000 0.001 0.006 0.031 0.0 I O 0.018 0.466 0.266 0.340 0.210 0.026 0.299 1.000

*Entries above lhe identity diagonal are vallles for coefficient of correlation r. Entries below the identity diagonal are vallles forr 2

Board Life Air Content (Lab)

Air Content (Field) Initial Penetration Reading

Normal Consistency Water Content (Lab)

Water Retention Comp. Stren~th (2 Day)

Set Time Unitial GiL) Set Time (Final Vicat)

Insoluble Residue Set Time (Final GiL)

Comp. Strength (7 Day) Comp. Strength (28 Day)

Fineness (-45 11m) Fineness (-2 um)

Set Time (Initial Vicat) Water Content (Field)

F10w Loss on !$nition

Me:O Content ~ False Set

Fineness (Blaine) Autoclave EXJJansion

S03 Content

=== iii

;; .. ~ ~

• -~'" ~ JIIIIII

~

-1 -0.8 -0.6 -0.4 -0.2 O 0.2 0.4 0.6 0.8 1 Fig. 2--Correlation Coefficients for Measured Variables Paired With Workabi!ity Rating.

W orkability Ratin~ Water Content (Lab)

Air Content (Lab) Normal Consistency

Air Content (Field) Initial Penetration Reading

Water Retention Water Content (Field)

F10w Comp. Strength (2 Day)

Fineness (-45 fIm) Insoluble Resldue Fineness (-2 um)

Set Time (lnitial GiL) False Set

MgO Content Comp. Strength (7 Day)

Comp. Strength (28 Day) Loss on Ignition

Set Time (Final Gil.) Set Time (Final Vicat)

Fineness (Blaine) Set Time (Initial Vicat)

Autoclave Expansion S03 Content

~== ~ ~ ~

_..��!

-1 -0.8 -0.6 -0.4 -0.2 O 0.2 0.4 0.6 0.8 Fig. 3--Correlation Coefficients for Measured Variables Paired With Board Life.

As one might expect, variables that are measurements made on the field mixed or laboratory mixed mortars tend to exhibit stronger relationships with workability and board !ife than do variables that are properties of cement pastes or of the cements themselves. Workability ratings correlate best with board !ife readings, air content (both laboratory and field air content) , and initial modified concrete penetrometer

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readings. A significant correlation is also indicated between workability and normal consistency. In reviewing the correlation coefficients, one must remember that the workability rating system adopted in this study assigned lower values to more workable mortars. The negative correlation coefficients between workability and board life workability and air content indicate that better workabi!ity ratings were generally assigned to monars having longer board life and higher air contents. The association of better workabi!ity and longer board !ife with lower water requirements for these mortars can be explained by the effect of air content on water demando

Initial penetration readings also exhibited a significant relationship to workabi!ity and board !ife. This probably reflects the fact that most of the variance in initial penetrometer readings was related to early stiffening tendencies of some of the mortars.

Analysis of the data also indicates a relationship between water retention and workabi!ity as well as between water retention and board !ife. The correlation coefficient is fairly low, but an F test indicates that the regression for water retention and workability is significant at the 1 % levei of confidence while the regression between water retention and board life is significant at the 2.5 % levei of confidence. Therefore, the linear regression model using water retention as an independent variable is at least a better predictor of workability and board life than the mean of those variables.

One can develop mathematical models exhibiting improved corre1ation coefficients by

Table 8 -- Multiple Linear Regression Correlation (Workability Rating as Dependent Variable)

including severa1 variables in -----------------;M-:-:-ul;:"u'""·p,.le--a multiple linear regression . Step Variab1e Entered Correlation Table 8 lists multiple R R2 coeffi~ients of correlation (R --;I---:2""""'B,-0-ar-d"""L;-,-,if'""e-------"0'""'. 7~8"'2=---:0"./6~1~1-and R ) obtained by multiple 2 6 Air Content (Lab) 0.834 0.696 linear regression analysis. 3 5 Initial Penetration Reading 0.866 0.750 Workability was the 4 13 Normal Consistency 0.868 0.754 de pe n d en t v a r i a b I e . 5 9 Water Content (Lab) 0.895 0.801 Independent variables were 6 7 Water Retention 0.895 0.801 added consecutively to the 7 10 Comp. Strength (2 Day) 0.902 0.813 multi pIe linear analysis 8 18 Set Time (Initial Gil.) 0.913 0.833 providing an indication of the 9 21 Fineness (-45 J.lm ) 0.920 0.847 effect of each additional variable. Table 9 presents similar information with board life as the dependent variable.

Comparisons of expected values for workability and board life using multiple linear regression models compared to measured values are shown in Figs. 4 and 5. Fig . 4 illustrates the lirnitations of the workabi!ity rating system, which constrained workability values to the integers I , 2, 3, and 4. A more precise rating system may have yielded improved correlation. More

Table 9-- Multiple Linear Regression Correlation (Board Life as Dependent Variable)

Step Variable Entered

1 6 Air Content (Lab) 2 5 Initial Penetration Reading 3 13 Normal Consistency 4 9 Water Content (Lab) 5 7 Water Retention 6 10 Comp. Strength (2 Day) 7 18 Set Time (lnitial Gil. ) 8 21 Fineness (-45 J.lm) 9 14 False Set 10 4 Water Content (Field) II 1 Workability Rating

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Multiple Correlation

0.722 0.521 0.754 0.568 0.807 0.651 0.816 0.665 0.822 0.675 0.824 0.679 0.883 0.780 0.899 0.808 0.937 0.877 0.942 0.888 0.957 0.916

consistent agreement between predicted and actual values is evident for the board life model multiple linear regression equation. However, regression analysis indicates relationships but does not confirm cause and effect. It should also be recognized that several of the variables included in the multiple linear regression analysis are interdependent. For example, lab water content, normal consistency, and air content would be expected to have some interdependence, and the correlation matrix indicates that this is so.

4.5 • 00% 4 c o 3.5 .= o-

3 '" 11 O:::-.q->, • 2 .5 . := E

:-::: 0 2 XX .o:::: '" 0 l.5 ..>:: ü • 6 ~ 1 xx ~J!.

0.5 t '-"

O I I

x x xx

• • Preclicted Workability •

X Actual Workablity xx X • • -I· .

xx X xx •• 1 xx xxx • •

I I I I I I I I I I I I I I I I I 1 3 5 7 9 II 13 15 17 19 21

Mortar Sample Number

Fig. 4--Comparison of Actual Workability Rating to Yalues Predicted by Multiple Linear Regression Equation (nine variables).

90 X X

'" 80+~ x ~ 70 • ~ ê • X • • ~ 60 X ~x X.

x x • Predicted Board Life , 50 . • • ·x ~ 40 X X X X~ :J X Actual Board Life -o 30 X 2 20 o X a:l 10

O X -: I I I I I I I I I

3 5 7 9 11 13 15 17 19 21

Mortar Sample Number

Fig. 5--Comparison of Actual Board Life to Yalues Predicted by Multiple Linear Regression Equation (eleven variables).

The correlation matrix also indicates a strong relationship between lab measured air comem and field measured air (r=0.911). Under the conditions of these tests, the field measured air averaged about three percent less than the air contem of laboratory mixed and tested mortars.

6. CONCLUSIONS

The following summarizes the results of this investigation:

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1. Factors exhibiting strong relationships to the workability of mortars included measured board !ife of field mixed mortar, air content of field mixed or laboratory mixed monar, and initial penetTation reading. A relationship between workability and air content has been previously documented [Skeen , 1957] but not quantitatively analyzed. 2. Laboratory measured water retention also exhibited a significant correlation to workability although not as stTong of a relationship as indicated for the two variables mentioned above. 3. Little correlation was noted between workability and setting time, false set, or properties of cementitious materiai s such as fineness. However, inclusion of setting time and false set in multiple linear regression analysis did slightly improve correlation to workability. 4 . Variables exhibiting a stTong relationship to workabi!ity tended to also exhibit a stTong relationship to board !ife. 5. The field measured air content of monars in this srudy averaged about 3% less than the air content of monars mixed and tested in accordance with ASTM C91.

Workability and board life are important performance properties of monar, panicularly from the perspective of the mason . The modified concrete penetrometer offers an effective means of evaluating board life of field monars; however, overall evaluation of workability remains subjective. This study indicates that most of the commonly measured propenies of laboratory mortars, properties of lab mixed cement pastes, or cementitious materiais are not effective in evaluating potential field workability of cementitious materiais used to produce masonry mortars. There is clearly a need for development of more precise measurement techniques in thi s area.

7. REFERENCES

I. Palmer, L. A. , and Parsons, D. A. , "Rate of Stiffening of Mortars on a Porous Base ," Rock ProdUClS, Vol. 35, No., 18, Chicago, USA , 1932, pp. 18-24.

2. ASTM, "A Preliminary Consideration of Some Proposed Methods of Sampling and Testing Mortar for Unit Masonry" , ASTM Bullelin . No. 94, October, 1938, Philadelphia, USA, pp. 40-46.

3. Conway, 1. T. , "A Method for Determin ation of Consistency and Consistency Retention (Board Life) of Masonry Mortars," Cemenl Concrele and Aggregares Journal, Vol . 2, No. 2, Philadelphia, USA , 1980, pp. 89-91.

4. Huizer, A ., Ward , M. A. , and Morstead , H., "Field and Laboratory Study Using Current and Proposed Procedures for Testing Masonry Mortar," Masonry: Pasl and Presem, ASTM STP 589, ASTM , Ph iladelphia, USA , 1975, pp. 107-122.

5. Huizer, A., "An Evaluation of Compression Prism, Shear Bond, and Bending Bond Control Test s for Clay Brick Masonry ," Canadian Journal of Civil Engineering , Vol. 3., No . 3 , Ottawa, Canada, 1976, pp. 402-408.

6. Skeen, J. W. , "Aerated Mortars ," The Nalional Bui/der. Vol. 36, No. 9, London , United Kingdom, 1957 , pp. 311-313.

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