Appendix_B_-_Fall_River_Entrance_Station_Mortar_Analysis_09_21_2021_0002.pdf
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- Solicitation number
- 140P2022R0005
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This document provides a mortar analysis for the Fall River Entrance Station in Rocky Mountain National Park. The analysis details the aggregate size distribution, binder ratios, and compressive strength of three mortar samples from the station. Sample 1 was taken from the low west end of the upper headwall, sample 2 from under the top course of the low headwall, and sample 3 from the curb of the parking lot. Aggregate sieve analysis showed samples 1 and 2 were slightly skewed toward larger aggregate sizes compared to ASTM C144 standards, while sample 3 aligned well. All samples contained a high percentage of fine material. The aggregate appeared to be native Colorado stone including quartz and granite. Binder ratios ranged from 24-28% dissolved Portland cement. Compression testing suggested sample 3 mortar was closest to ASTM type N, while samples 1 and 2 were recommended as type O.
The related federal contract opportunity is solicitation number 140P2022R0005 to replace the undersized Fall River Entrance Station at Rocky Mountain National Park for the Department of the Interior National Park Service National Office.
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Mortar Analysis
Prepared For:
JVA, INc
1319 Spruce Street
Boulder, co 80302
Project:
fall river entrance station rocky mountain national park
Prepared By:
Phillip Barlow, Historic Preservation specialist
Barlow CULTURAL RESOURCE CONSULTING, LLC
4576 Tanglewood Trail, Boulder, CO 80301
303-746-1602 : BARLOWPL@GMAIL.COM
September 21, 2021
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CONTENTS
EXECUTIVE SUMMARY
COMPOSITION ANALYSIS
AGGREGATE SIZE DISTRIBUTION
MICROSCOPIC ANALYSIS
COMPRESSION ANALYSIS
MORTAR MIX RATIOS
COLOR MATCHING
APPENDIX
MORTAR ANALYSIS FOR RATIO AND AGGREGATE DISTRIBUTION PROCEDURE
AGGREGATE DOCUMENTATION
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EXECUTIVE SUMMARY
Three mortar samples from site elements at the Fall River Entrance Station to Rocky Mountain National Park were collected by Tom Soell of JVA, Inc. and delivered to BCRC on September 16, 2021. The Fall River Entrance Station was built ca.1930 as a Civilian Conservation Corps (CCC) project in conjunction with the National Park Service. The three samples were labeled as follows:
1: Low on the west end of the upper headwall 2: Under top course of the low headwall 3: Curb at parking lot
This intent of this report is to provide the necessary information that will allow a mason to create a mortar mix that will match the existing in a historically appropriate manner. The specifications include a mortar mix ratio, a detail of aggregate grain size and color, and a methodology for creating an accurate mortar color match.
Aggregate sieve analysis of sample 3 aligned well with ASTM C144, standard for masonry mortar aggregate.
Samples 1 and 2 were skewed slightly towards larger aggregate. A high percentage of fine material was present in all samples, likely indigestible components of the cement binder, clays, and pigments. The aggregate in all four samples appear to be native to Colorado and include clear quartz, cloudy white quartz, orange and green quartz, and granite. Aggregate shape is primarily sub-angular.
Standards published by the American Society for Testing and Materials (ASTM C270) specifies that cement/lime/sand mortars should have a sand content of at least 2.25 times the lime/cement mix (31% binder), and not more than 3 times the binder mix (25% binder). All three samples were within, or very close to, the standard.
The mortar samples were taken from stone construction, with the stone likely being predominantly granite.
Due to the durable nature of granite and the exposed location, a type O mortar is recommended for areas represented by samples 1 and 2. Sample 3 was more difficult to crush and resisted acid digestion significantly more than the other samples, indicating that it had a higher strength and percentage of Portland cement.
Compression testing of sample 3 suggests that this mortar was closest to the type N category.
Sample
Sample Name % Dissolved Portland Cement
Hydrated Lime
Sand Mortar Type
1 Low on the west end of the upper headwall
28% 1 2 8 O
2 Under top course of the low headwall
25% 1 2 9 O
3 Curb at parking lot 24% 1 1 6 N
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COMPOSITION ANALYSIS
Before acid digestion a qualitative hardness test is performed to determine the presence of cement. A pure lime mortar, which is just lime and sand, will typically crush with minimal effort. If a significant effort is required to fracture the sample then it is safe to assume that Portland cement is part of the mortar mix.
Samples 1, 2, and 3 could not be crushed with finger strength, indicating that cement was present.
A digestive mortar analysis was conducted on the material, the full procedure for which is available in the appendix. Acid digestion is the process of using acid to dissolve lime and cement. By measuring the weight of the sample before and after digestion it is possible to determine the ratio of binder to aggregate.
Following digestion the aggregate is washed, filtered, and sieved. This determines the gradation of aggregate sizes.
A U.S. Standard sieve set was used to calculate the proportion of grain sizes. The sieve sizes used were:
No. 4 – opening of .187” No. 8 – opening of .09” No. 16 – opening of .046” No. 30 – opening of .023” No. 60 – opening of .0098” No. 100 – opening of .0055” No. 200 – opening of .0029”
Pan - This is the material that was small enough to pass through the 200 sieve. Fines are generally clay or very fine aggregate material, including pigment that is smaller than .0029”.
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AGGREGATE SIZE DISTRIBUTION
Sample # 1
Sample Location Low on the west end of the upper headwall
Name Fall River Entrance Station
Date 09.17.2021
Sieve With Sand
Without Sand Sand
Particle sizes % of total
4 61.72 61.72 0 >4.75mm 0% gravel
8 58.22 57.81 0.41 <4.75 mm 7% very coarse sand 16 57.52 56.71 0.81 <2.36 mm 14% coarse sand
30 55.23 53.6 1.63 <1.18 mm 29% medium coarse sand 60 56.01 54.62 1.39 <.60 mm 24% medium fine sand
100 53.57 53.14 0.43 <.3 mm 8% fine sand
200 53.14 52.82 0.32 <.15 mm 6% very fine sand
Pan 14.36 13.67 0.69 <.075 mm 12% silt
Total 409.77 404.09 5.68
Weight of sample
7.87 grams % dissolved 28%
Wt filter paper for sand 1.43 grams
Wt sand & paper
7.11 grams Wt sand
5.68
% sand
72%
0%
7%
14%
29%
24%
8% 6%
12%
0%
5%
10%
15%
20%
25%
30%
35%
% of total
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The following table compares this data to the ASTM C 144 standard for masonry mortar aggregate. Red indicates that the sample does not match the standard.
Sieve Size Percent Passing, SAMPLE #1
ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 93 95-100%
No. 16 79 70-100%
No. 30 50 40-75%
No. 40 26 10-35%
No. 100 18 2-15%
No. 200 12 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, pigments, and indigestible portions of Portland cement and not considered part of the aggregate.
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Sample # 2
Sample Location Under top course of the low headwall
Sand Sand
Particle sizes % of total
4 61.71 61.71 0 >4.75mm 0% gravel
8 58.57 57.81 0.76 <4.75 mm 7% very coarse sand 16 58.38 56.72 1.66 <2.36 mm 16% coarse sand
30 56.43 53.6 2.83 <1.18 mm 27% medium coarse sand 60 57.42 54.61 2.81 <.60 mm 26% medium fine sand
100 54.07 53.14 0.93 <.3 mm 9% fine sand
200 53.3 52.82 0.48 <.15 mm 5% very fine sand
Pan 14.88 13.71 1.17 <.075 mm 11% silt
Total 414.76 404.12 10.64
14.16 grams % dissolved 25%
Wt filter paper for sand 1.39 grams
12.03 grams
10.64
75%
0%
7%
16%
27% 26%
9%
5%
11%
0%
5%
10%
15%
20%
25%
30%
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ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 93 95-100%
No. 16 77 70-100%
No. 30 50 40-75%
No. 40 24 10-35%
No. 100 15 2-15%
No. 200 11 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 9
Sample # 3
Sample Location Curb at parking lot
Sand Sand
Particle sizes % of total
4 61.71 61.71 0 >4.75mm 0% gravel
8 58.06 57.8 0.26 <4.75 mm 2% very coarse sand 16 57.51 56.72 0.79 <2.36 mm 6% coarse sand
30 56.7 53.6 3.1 <1.18 mm 25% medium coarse sand 60 60.08 54.61 5.47 <.60 mm 44% medium fine sand
100 54.14 53.15 0.99 <.3 mm 8% fine sand
200 53.22 52.81 0.41 <.15 mm 3% very fine sand
Pan 14.97 13.66 1.31 <.075 mm 11% silt
Total 416.39 404.06 12.33
16.13 grams % dissolved 24%
Wt filter paper for sand 1.4 grams
13.73 grams
12.33
76%
0% 2% 6%
25%
44%
8% 3%
11%
0% 5%
10% 15% 20% 25% 30% 35% 40% 45% 50%
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ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 98 95-100%
No. 16 92 70-100%
No. 30 67 40-75%
No. 40 23 10-35%
No. 100 15 2-15%
No. 200 11 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 11
MICROSCOPIC ANALYSIS
The aggregate from all three samples is similar and composed of sub-angular clear and cloudy white quartz throughout the size gradations with a small mix of various colored inclusions, including orange and green quartz, and granite. The overall hue of the aggregates is beige. All of the minerals are local to this region of Colorado. Images of the aggregate from each sample are included in the appendix for reference.
Image 1: Representative image of aggregate.
1 Powers, M.C., 1953, Journal of Sedimentary Petrology, v.23, p. 116
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COMPRESSION ANALYSIS
Test procedure:
A portion of each supplied sample was selected for testing and the dimensions for each were recorded
The sample was placed on a 56Kn point load tester equipped with a ball-seated flat platen to allow for proper seating
The sample was compressed until failure and the peak pressure recorded
The compressive strength was determined and converted to the PSI standard
NOTE: Sample 3 (Curb) was the only sample of sufficient size to conduct compression testing.
Sample # 3
Sample Location Curb at parking lot
Sample Height
(mm) 14.45
Sample Width (mm) 23.46 Sample Depth (mm) 27.43
Max Kn at failure 2.654
Kn/sectional area 0.005088598
PSI 738.0387235
Mortar Type Per
ASTM C270
Min.
Compressive Strength
M 2500 psi S 1800 psi N 750 psi O 350 psi K 75 psi
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MORTAR MIX RATIOS
Standards published by the American Society for Testing and Materials (ASTM C270) specifies that cement/lime/sand mortars should have a sand content of at least 2.25 times the lime/cement mix (31% binder), and not more than 3 times the binder mix (25% binder). All three samples were within, or very close to, the standard.
The mortar samples were taken from stone construction, with the stone likely being predominantly granite.
Due to the durable nature of granite and the exposed location, a type O mortar is recommended for areas represented by samples 1 and 2. Sample 3 was more difficult to crush and resisted acid digestion significantly more than the other samples, indicating that it had a higher strength and percentage of Portland cement.
Compression testing of sample 3 suggests that this mortar was closest to the type N category.
Sample
Sample Name % Dissolved Portland Cement
Hydrated Lime
Sand Mortar Type
1 Low on the west end of the upper headwall
28% 1 2 8 O
2 Under top course of the low headwall
25% 1 2 9 O
3 Curb at parking lot 24% 1 1 6 N
Mortar Types (Measured by volume)
Designation Cement Hydrated Lime or Lime Putty
Sand
M 1 1/4 3 - 3 ¾
S 1 1/2 4 - 4 ½
N 1 1 5 – 6
O 1 2 8 – 9
K 1 3 10 – 12
"L" 0 1 2 1/4 – 3
Suggested Mortar Types for Different Exposures
Exposure
Masonry Material Sheltered Moderate Severe
Very durable:
granite, hard-cored brick, etc.
O N S
Moderately durable:
limestone, durable stone, molded brick
K O N
Minimally durable:
soft hand-made brick
"L" K O
2 Technical Preservation Services, National Park Service. “Repointing Mortar Joints in Historic Masonry Buildings” 1980 http://www.cr.nps.gov/hps/tps/briefs/brief02.htm http://www.cr.nps.gov/hps/tps/briefs/brief02.htm
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COLOR MATCHING
Once an aggregate has been selected several small (roughly 1 cup) test batches should be mixed in the prescribed ratios. Matching the color as closely as possible with the aggregate is the best approach, but this testing period is when various pigments and additives can be tried to determine how best to match the existing color. Volcanic pumice, lamp black, and bone black are all chemically stable coloring agents that resist fading in the sun.
Using a masonry specific pigment, each test batch should be mixed with varying quantities and combinations of pigment to produce a palette of choices. It is important that each batch be labeled, and that precise notes are kept of the pigment recipe. Once allowed to dry the building owner or project manager should inspect the samples and select the one that best matches the remainder of the wall. The recipe for that sample should then become the master recipe for the project. It is important to note that mortar color can be different from one part of the wall to another, so if a discernible difference in color is noted as work progresses than the recipe should be altered to maintain uniformity.
Matching the new mortar to the existing will be a challenge because of the discoloration of the original mortar from dirt and plant growth. Options to address this include:
Match the new mortar to the original and let the discoloration occur naturally
Match the new mortar to the existing, keeping in mind that the pigments might weather differently
Clean the masonry to remove the discoloration
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APPENDIX
Mortar Analysis for Ratio and Aggregate Distribution Procedure
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AGGREGATE DOCUMENTATION
Image 2: Sample 1, representative aggregate
Image 3: Sample 1, , representative aggregate
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Image 4: Sample 2, representative aggregate
Image 5: Sample 2, representative aggregate
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Image 6: Sample 3, representative aggregate
Image 7: Sample 3, representative aggregate
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