24. Geology Study-Investigation (1997) (Ref Only).pdf

Geo technical Engineering

Construction Materials Testing

Construction Engineering

Inspection

Hydrogeol ogy

GCI

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PRELIMINARY STUDY

PLAN DEVELOPMENT & MANAGEMENT

OF ROCK QUARRIES

ASCENSION AUXILIARY AIRFIELD

SOUTH ATLANTIC OCEAN

Environmental Engineering

Site Assessment

Asbestos Management

Site Remediation

GEOTECH CONSULTANTS INTERNATIONAL, INC.

CONSULTING ENGINEERS

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To:

GEOTECH CONSULTANTS INTERNATIONAL, INC.

AJT & Associates, Inc.

101-George King Boulevard Cape Canaveral, Florida 32920

Attention: Mr. Lou Mized, PE Manager, Engineering

June 10, 1997 Project No. G97-236

Subject: Prel1minary Study, Plan Development and Management of Rock Quarries, Ascension Auxiliary Airfield (AAAF) , South Atlantic Ocean

Dear Mr. Mized:

As requested and in accordance with our proposals dated January 23, 1997 and March 21, 1997 / we have completed a preliminary evaluation of existing rock mining quarries and facilities at the Ascension Auxiliary Airfield (AAAF) . The purpose of this study is to evaluate the existing aggregate quarries and mining operations and to assist in developing a comprehensive plan for the restoration and management of the existing quarry sites.

This report presents the observations made during our site reconnaissance (February 5 through February 14, 1997), our preliminary evaluation of the existing Island materials from a qualitative -standpoint, with our recommendations for a comprehensive -laboratory testing program to develop mix design criteria for concrete production. This report also presents our preliminary - - -suggestions and recommendations for future exploitations to meet the projected aggregate needs at the Island.

I 2265 Lee Road, Suite 123 • Winter Park, FL 32789 • Tel: (407) 644-4846 • Fax: (407) 628-0113

Ascension Island June 1.0,. 1.997

We appreciate the opportunity to be of service to you on this study and trust that the information provided herein is sufficient for your immediate needs. If you have any questions regarding the contents of this report or should we be of further assistance please do not hesitate to contact the undersigned.

Sincerely 1

GEOTECH CONSULTANTS INTERNATIONAL, INC.

Fernando Parra 1 PhD Sr. Project Engineer

Owusu Aman;1 Sr. Engineer

TABLE OF CONTENTS

EXECUTIVE SUMMARY

INTRODUC';r'ION

SCOPE OF SERVICES

GEOLOGY

ISL.AND MATERIALS

On-Base Rock Sources

Rock Quarry Receiver Antenna Field Mining Area

Off-Base Rock Sources

Current Use Of Island Materials

Basaltic Rock Aggregates Black Cinder Material Red Volcanic Cinder Island Sand

Quality Of Island Materials

Previous Studies

SUITABILITY REQUIREMENTS FOR CONCRETE AGGREGATES

Grading Particle Shape and Surface Texture Unit Weight and Voids Specific Gravity Water Absorption Wetting and Drying Properties Abrasion and Skid Resistance Strength of the Aggregates Resistance to Chemical Attack Deleterious Substances / Alkali Reactivity l

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TABLE OF CONTENTS (CONT'D)

ENGINEERING EVALUATION l6

Preliminary Evaluation l6

Supplemental Evaluation l7

Mining Operations l8

On-Going Rock Mining Operations Alternate Rock Mining Procedures On-Going Cinder Mining Operations

RECOMMENDATIONS FOR FUTURE EXPLOITATION

General

Future Equipment Needs

Environmental Impact & Reclamation Issue.s

SUMMARY AND FINDINGS

REPORT LIMITATIONS

REFERENCES

TABLES

CURRENT MINING CHARACTERISTICS

CHARACTERISTICS AND TESTS OF AGGREGATES

GRADING REQUIREMENTS FOR COARSE AGGREGATES (ASTM C-33)

HARMFUL MATERIALS IN AGGREGATES

POTENTIALLY HARMFUL REACTIVE MATERIALS

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TABLE l

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE OF CONTENTS (CONT'D)

FIGURES

VICINITY MAP FIGURE l

ISLAND MAP FIGURE 2

GEOLOGIC MAP OF ASCENSION ISLAND FIGURE 3

LOCATION OF MINING AREAS FIGURE 4

EXISTING ROCK MINING AREAS FIGURE 5

BASALTIC ROCK SAMPLES FIGURE 6

EXISTING BLACK AND RED CINDER QUARRIES FIGURE 7

EXISTING MINING EQUIPMENT FIGURES 8 & 9

SIGNS OF DETERIORATION OF EXISTING STRUCTURES FIGURES lO & ll

APPENDICES

PREVIOUS STUDIES BY OTHERS APPENDIX A

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EXECUTIVE SUMMARY

The scope of the services for this preliminary study consisted of a literature review and site reconnaissance to evaluate the general site conditions as well as the availability and suitability of the island materials. The study focused primarily on on-base aggregate sources as well as off-base sites for future island-wide (British and US) exploitation. We also reviewed the current mining procedures and equipment needs to establish the logistics for future exploitation to meet the anticipated aggregate needs at the Island.

Based on the data gathered during this preliminary study, it appears that there are adequate reserves of rock to support the future development needs of the Island for the next 20 years or more. The results of previous petrographic analyses and other geologic considerations by others indicate that the basaltic rock aggregates at the Island could be used for structural concrete as long as additional studies are performed to determine the engineering and chemical properties of the rocks. The studies reviewed indicate that there may be a need for low-alkali cement, and/or adding pozzolans or other admixtures to counteract potential alkali reaction in the rocks.

It is our opinion that stockpiled material at both the existing quarry and antenna field areas could be used for aggregate production for the next 2 to 3 years. When this stockpiled material has been depleted, we recommend that further exploitation should be limited to the existing rock quarry area.

Our preliminary estimates indicate that expanding the existing mine another 100 feet to the north and 50 feet to the east could yield approximately 20,000 cubic yards of basaltic rock.

Preliminary corrosion series tests have been performed to determine the environmental classification of the black and red volcanic cinder materials. The test results are consistent with those of 11 slightly aggressi ve 11 soils, per FDOT environmental classification criteria. The slightly aggressive nature of these soils may be partly responsible for various anomalies (spalling, cracking, segregation, etc.) observed in the concrete structures constructed in or backfilled with these materials. Further testing and evaluation will be required to provide appropriate recommendations for concrete structures in contact with these soils. The compaction properties, gradation and other geotechnical parameters of these materials need to be properly defined to support the use of these soils as structural fill.

It appears that no environmental impact studies have been performed to support the current and future rock and cinder mining operations on the Island. We recommend that such study be undertaken as part of our site selection process and also to provide a basis for developing appropriate mining procedures and

Executive Summary Page ii site reclamation plans for the selected rock mining area and the existing cinder quarry sites. The implementation of properly designed mining procedures at the cinder material sites is of particular concern. The presence of vertical quarry pit walls (notably at the black cinder quarry) poses a slope failure risk which should be addressed immediately.

INTRODUCTION

The purpose of this preliminary st~dy is to evaluate the sou~ces of construction materials on Ascension Island and to determine the most economical way of obtaining coarse aggregate for use on the Island.

Ascension Island is located in the South Atlantic Ocean, half-way between Africa and South America (about 375 miles from either continent) and about 375 miles south from the Equator. Its approximate coordinates are longitude 07° 57' South and latitude l4° 24' West. Ascension Island is small, volcanic, hilly and has the appearance of a rough circle with a diameter of about 6 miles and an area of 34 square miles. A vicinity map is provided in the attached Figure l.

Ascension Island was first discovered by Juan Da Nova in l50l. It appears that this event went unnoticed and the place was rediscovered by Alphonse D'Alburquerque two years later. He named it Ascension. The Island was practically uninhabited until l8l5, when the British claimed it for King George III. It has been a British naval possession since then. The United States of America (USA) has leased part of the territory. An airfield and a NASA tracking station (now closed) were constructed in l942 and l967, respectively. The current population is about l,250. The Island is nominally governed by a resident Administrator, but actually the place is run and operated by its users. The site, defined as a "closed" island, is inaccessible to casual visitors. Only the United States Air Force (USAF) and Royal Air Force (RAF) airplanes and the Royal Mail Ship stop there.

The terrain is essentially inhospitable, dry, arid, rugged and barren. Some vegetation has grown in the last few years around Green Mountain, though. The topography is varied, being higher and more rugged in the central and eastern parts of the Island. The remainder of the Island eastern and southern perimeter is made-up of steep inclines originating from Green Mountain to vertical bluffs to the sea. A series of hills exists, ranging from l,000 to 2,500 feet above sea level. Green Mountain is the highest one.

Most of the Island is covered with ancient lava flows and cinder cones. An Island map is provided in the attached Figure 2.

There is little rain at the Island. Precipitation (about 6 inches per year in the lower coastal areas around Georgetown and the US base) does not follow any specific cycles. Rains may be quite intense at times. The highest precipitation values (about 30 inches per year) have been recorded at the Green Mountain. March and April are the warmest monthsi September is the coolest. Mean yearly, maximum and minimum temperatures are 77° F, 87° F and 74° F, respectively. Continuous winds blow from the SE at a speed of about l5 knots. The average relative humidity is 72~.

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Ascension Island

SCOPE OF SERVICES

The scope of services for this preliminary study consisted of a literature review and site reconnaissance to evaluate the general site conditions as well as the availability and suitability of the Island raw materials. The study focused primarily on aggregate sources, located on and off-base, for future Island-wide (British and US) exploitation. We also reviewed the current mining procedures and equipment needs to establish the logistics for future exploitation and to meet the anticipated aggregate needs at the Island. The objectives of this study were accomplished as follows:

• A literature review focused on identifying sources of natural materials such as concrete aggregate and fill soils for construction of building structures and pavement sections.

This process included a review of available surface and subsurface data such as geologic and topographical maps, aerial photographs, published studies and other available pertinent information. Our literature review also included an evaluation of available prospection records and production capacities, including the adequacy of existing facilities to support production for the proposed projects at the Island.

Available test results on the quarry materials were also reviewed.

• A field reconnaissance of the Island was conducted during the period of February 5 through February 14, 1997 to familiarize our staff with the general site conditions and on-going mining operations as well as other features that may impact future exploration and studies. Existing structures and facilities built on or of various island materials were inspected by our staff. These structures included existing buildings supported on borrow soils (red cinder) or sidewalks and other concrete pavement sections constructed using on-base aggregates.

• Inspection of existing rock collection and crushing equipment and meetings with the base equipment maintenance staff to determine the suitability of the existing mining, processing and transportation equipment.

• Representative samples of the island materials were collected for a preliminary and limited laboratory testing program. The testing consisted mainly of corrosion series tests to determine the environmental classification of the red and black volcanic cinder materials.

Ascension Island

During the next phase of the ~tudy, we envision to conduct a comprehensive laboratory testing program on the rock samples collected in this preliminary phase as well as future exploration to provide a basis for more specific guidelines for concrete mix design.

• The data collected in our literature review together with the findings of our field reconnaissance and limited laboratory testing were evaluated to provide our preliminary opinions regarding the most economical method of mining the island materials for use in future construction projects.

Subsequent sections of this report contain more detailed descriptions of the locations, nature and characteristics of the various island materials.

GEOLOGY

The Island is located on the geologic feature known as the nMid Atlantic Ridgen, consisting of a belt of submarine mountains that runs from Iceland to Antarctica, nearly midway between the continents. It is of volcanic origin and represents the very tip (and therefore the youngest part) of a volcanic edifice that developed on top of the oceanic crust of the South American Plate.

According to Packer (1993), at least three major phases of volcanic activity have occurred. An early period during which Green Mountain, White Hill, Weather Post, South East Head and Boatswain Bird island vents were formed. After a possible dormant period, a second period occurred that led to the formation of Spoon Crater, Traveller's and Mountain Red Hills. More recently, new episodes originated the Sister Peak Complex, South Gannet Hill 1 etc.

Volcanic activity is ndormant 11 at this time. Any evaluations about possible future activity are beyond the scope of this report. ·

Two basic types of volcanic materials can be discerned at the Island, namely pyroclastic deposits and lava flows. According to the geologic literature reviewed, pyroclastic deposits and (trachyte) lava flows and domes are found on the central and eastern parts of the Island. Scoria flows and (mafic) lava flows (some with a thin veneer of pyroclastic deposits) prevail in the rest of the territory. Basaltic lava flows seem to prevail in the southern part of the island 1 according to our interpretation of a geological map 1 originally produced by Nielson and Sibbet (referenced in Weaver 1 1987) / and modified and simplified by Weaver (1987) .

Scoria cones are composed mainly of cinders, with presence of blocks and globs of molten rock. The material is either black or red colored (oxidized) . Mafic lava (basalt and benmoreite) flows

Ascension Island are a few feet thick and erupted along breached cones. The material is scoriaceous. Pyroclastic deposits are composed of scoria and pumice. Trachyte and rhyolite flows are more common in the central and eastern parts of the Island.

A brief description of materials as cited in the searched· literature follows. Some of them were actually observed during our field reconnaissance. A geologic map of the Island is provided in the attached Figure 3.

ISLAND MATERIALS

Although the geologic literature review identifies numerous material types from a variety of lava flows and volcanic activity at the Island 1 current use of island materials appears to be limited to four (4) main types of rock 1 aggregates and/or fill soils 1 namely 1 Basaltic Rock Aggregates; Red Volcanic Cinder; Black Volcanic Cinder and Island Beach Sand. The following sections address on-base/off-base sources of aggregate as well as the current use of the Island materials.

On-Base Rock Sources

This material consists of basalt and basaltic scoria rock 1 crushed into concrete aggregate for use mainly in concrete pavement applications on the Island. The rock is mined primarily from two

(2) on-base locations and previously from the existing off-base British stone quarry. The two(2) main on-base sources of rock are the rock quarry and the receiver antenna field mining areas.

Rock Quarry

The existing rock quarry is located at the south end of southwest bay 1 at the southwest side of the leased property.

The quarry site is approximately 2 to 3 acres in plan area and extending 15 to 30 feet below existing grade. Mining in this area has consisted of excavations and ripping of large blocks of rock (3 1 or more in diameter) that are subsequently broken (using a truck-mounted hammer) into small sizes 1 loaded into trucks and transported to the existing crusher.

The quality of rock from this location appears to be relatively superior 1 with approximately 85%" to 90%" of the dense basaltic rock and only 10%" or so of the porous basaltic scoria rock type. We estimate the available stockpile of rock in the quarry area to be approximately 500 to 700 cubic yards.

There is a potential for an additional 20 1 000 cubic yards of rock from the quarry if mining is extended another lOO ·to 150 feet to the north and east of the current limits of the mine.

Receiver Antenna Field

This surface rock mining operation area is located in the southwest quadrant of the U.S. leased property, on the southwest side of Cotar Hill and the existing airfield.

Mining operations in this area consist of scavenging or gathering of surface basaltic rock which is then crushed for aggregate. The rock gathering operations are conducted from the ocean along the property lease line and landward toward Antenna No. 2. Access roads (covered with red volcanic cinder material) have been opened into the mining area for transportation of rock to the crusher. Surface stone and rocks are bulldozed to the perimeter of the access roads and broken as necessary prior to collection and transportation to the crusher.

Based on visual inspection, we estimate the available quantity of rock within the immediate vicinity of the existing access roadways to be on the order of 2,000 to 2,500 cubic yards.

If the mining operations are extended another 50 to 70 feet away from the existing vehicular access roads, we estimate that an additional 2,500 to 3,000 cubic yard of rock could be collected.

Based on visual inspection, we estimate the composition of the antenna field material to be approximately 60% of dense basaltic rock and 40% of porous basaltic scoria.

An alternate receiver antenna mining area was identified as a potential source of rock within the U.S. lease property. This area could be considered as an upland extension of the HSouthwest" receiver antenna surface mining area. Outcrops of basaltic rock similar to that in the existing surface mining area were identified on the northern side of Antenna No. 2, extending towards Cotar Hill. The area has fractured surface rock with approximately 50% of dense basaltic rock and 50% of porous basaltic scoria.

Exploitation in this area will, however, require vehicular access roads. Based on a conceptional plan, a 4,000 to 5,000-foot long access road should be constructed into the area. Also, based on field observation, we estimate that approximately 3,000 to 5,000 cubic yards of rock could be collected within the immediate vicinity of the proposed access road. Of this total volume, approximately 500 to 700 cubic yards of rock is already stockpiled from the construction clearing operations at Antenna No. 2.

Presented in Table 1 is a comparison rock/aggregates, quantity estimates, disadvantages, mining methods and a of the rock composition.

Off-Base Rock Sources of on-base sources of site advantages and general description

The British stone quarry has served as the primary Island aggregate source in the past. This quarry is located along the northern side of the airfield and has a stockpile of large basaltic rock from previous mining operations. While the British quarry has the capacity to supply the Island 1 s rock needs for several years, it is currently off-limits for American use. The British quarry still remains, in our opinion, the most suitable single source of aggregates for the Island.

Other potential off-base sources of rock were explored. These included the British Broadcasting Corporation (BBC) repeater station at the north of the Island, the Northeast Two Boats area, Central Island Green Mountain and the Green Mountain foothills and the East Island NASA facilities. While we found potential quarry and/or surface mining sites in these off-base locations, the disadvantages appear to out-number the advantages for future exploitation for production of construction aggregates. These disadvantages include distance from the property, access conditions, proximity of residential areas and the quality of rock.

The existing rock quarry locations are shown in the attached Figures 4 and 5. Samples of the Island basaltic rock are shown in the attached Figure 6.

Current Use Of Island Materials

Basaltic Rock Aggregates

It is our understanding that the current use of Island basaltic crushed rock aggregates has been limited to concrete mixes for various minor projects. Use of island aggregate appears to have been limited to concrete pavement sections, sidewalks and other low structural strength concrete applications. The conditions of these structures appear to vary from good to poor. Noticeable types of concrete deterioration include cracking, spalling, and disintegration.

Sound concrete slabs with no perceptible signs of distress were also observed.

Ascension Island

From our meetings with base construction services staff, we learned that most of the concrete mixes were made with limited design criteria. Sea water and unwashed island sand have been used in many of the concrete mixes. Observed anomalies in most of the existing concrete structures could be attributed to a variety of factors, including the above-mentioned. We also learned that the base has imported aggregates for all the major construction projects on the Island.

Black Volcanic Cinder

As indicated in the geologic data, the Island has numerous scoria cones composed of cinders and blocks. Black volcanic cinder is mined from a quarry at the Northwestern foothill of Gannet Hill, adjacent to the airfield runway. The quarry covers a plan area approximately 300 feet by 300 feet. The quarry site is shown in the attached Figure 7.

A backhoe is used to excavate the material which is then loaded into trucks for use on the Island. The Black cinder material is used mainly as a surface dressing on roadway sections and in landscaped areas around buildings. The quarry is about 3 O feet deep. The inclination of the sidewall varies from 25° to 50° in the central and southern sections to vertical along the north perimeter.

The Black cinder is highly porous material. It does not appear to have the abrasive and strength characteristics for use as a roadway surface course material or structured fill material. Further testing will be required to quantify the engineering properties for functional uses of the material.

Red Volcanic Cinder

Adjacent to the Ascension Auxiliary Air Force (AAAF) main base is a 500-foot high red cinder hill known as Southwest Bay Red Hill. A large portion of this hill is located within the leased property. Material from the hill is used as fill and surface dressing on vehicular access roads throughout the Island. The quarry site is shown in the attached Figure 7.

The gradation of the material varies from coarse to very fine. The color varies from red to reddish-brown or brown.

The Southern flank of the hill is being excavated from the base for the red cinder material. Terracing cuts into the hill have been made with a hillside slope inclinations of 45° to 60°.

Although the red cinder material is being used throughout the Island for various fill and surface dressing purposes, our literature review does not indicate any testing performed to quantify the strength properties and engineering characteristics of the material.

Our inspection of existing concrete structures, where red cinder fill material has been placed, indicates conditions of concrete deterioration (such as spalling, cracking, etc) .

This may be attributed to a chemically aggressive subgrade soil. Preliminary corrosion series tests performed on samples of the red cinder material indicate a "slightly aggressive" environmental classification. The results of these tests are presented and discussed in detail in subsequent sections of this report. Additional gradation and strength property tests will be required to quantify the basis for use of the material as structural fill.

Island Sand

Island sand is found along limited beach fronts and small sand pockets on the Island. There are no known sand deposits on the U.S. leased property except on the beach. The British quarry, located at the north side of the eastern end of the existing runway, has limited sand deposits mixed with a relative high amount of clay and silt.

Although the Ascension beach sand has been used in the past in various concrete mixes, it is AAA.F base policy not to remove beach sand for construction purposes. Ascension is a nesting ground for the Green (Chelonia Mydas) and Hawkbill (Eretmochelys Imbricata) sea turtles. Continued removal of beach sand could seriously affect the survival of these turtle species.

Quality Of Island Materials

The scope of this preliminary study does not include a detailed laboratory testing program to determine the suitability of the Island materials from an engineering/ chemical standpoint. However, we performed limited testing of the red and black volcanic cinder material to determine the environmental classification of these materials. The number, types and results of the corrosion series tests are summarized as follows:

ENVIRONMENTAL CLASSIFICATION FOR CINDER MATERIAL

Sample Material pH Resistivity Chlorides Sulfates Classification No. (ohm-cm) (ppm) (ppm)

1 Red Cinder, 7.2 8,900 60 < 5 Slightly North End Aggressive

2 Black 7.3 10,000 60 7.2 Slightly Cinder Aggressive

3 Red Cinder, 7.3 4,600 135 44.4 Slightly NE of Water Aggressive

Tank

4 Black 7.5 5,200 60 14 .4 Slightly Cinder Aggressive Quarry

* Environmental Classification is based on FDOT Structures Design Guidelines, Topic No. 625-020-107-h, Section 7.2.

In the absence of a comprehensive field and/or laboratory test results, our evaluation of the materials was limited to an assessment of the availability of construction materials on the Island. To provide a preliminary evaluation of the chemical and engineering properties of the materials, we reviewed and compiled the results of all available field and/ or laboratory testing results on the island materials. However, more detailed field and laboratory testing as well as engineering evaluation are needed to provide design level recommendations.

Previous Studies

A study was done by ATEC Associates in l990, for the Consolidated Instrumentation Facility (CIF) and radar areas, located at Cotar Hill (south of the airfield) . Thirteen borings were performed, to depths ranging from l5 to 70 feet. Standard Penetration Tests (SPT) were performed in each hole and samples were recovered to run grain size analyses, natural water content, content of fines and direct shear tests (for assessing slope stability conditions) . The results of the exploration indicated the presence of volcanic rock and tan, brown, red and (more frequently) black cinders, ranging in size from sand to gravel. The soils exhibited medium to loose density, natural moisture contents ranging from 0.6% to 37.9% and a fines content ranging from 3.5% to l7.l% were reported. The angle of internal friction was tested to be on the order of 48°.

The groundwater table was not encountered at the borings. Only four (4) sets of Atterberg Limit tests were done. The results indicate low plasticity inorganic silty soil (ML) . The results are summarized in the following Table.

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Ascension Island

ATEC (1990)

CONSOLIDATED INSTRUMENTATION FACILITY

Number of Borings 13

Depth (ft) 15-70

Strata Volcanic rock and cinders (sand to gravel sizes)

Classification (Finer Material) Inorganic silty soil (ML)

Relative Density Medium to Loose

Ground Water Table Not encountered

Natural Moisture Content ( %") 0.6-37.9

Fines Content ( %") 3.5-17.1

Angle of Internal Friction 48 (degrees)

A coarse aggregate testing program was also carried out, including petrographic examinations of thin sections. Relevant results are summarized as follows:

ATEC (1990)

CONSOLIDATED INSTRUMENT FACILITY

TEST RESULTS

Dry Unit Weight (pcf) 88.5 to 88.6

Specific Gravity 2.458

Absorption ( %- ) 3.4 - 3.6

Los Angeles Abrasion ( %- ) 29.2

Chloride Ion Content ( %- ) 0.0

Potential Reactivity Rc=275 millimoles/liter Sc=62 0 millimoles/liter Alkaline Reaction:

Potential Deleterious

ATEC (1990)

CONSOLIDATED INSTRUMENT FACILITY (CONT'D)

TEST RESULTS

Petrography Significant amounts of volcanic glass and cristobalite (reactive agents with alkalis in cement) .

No mention is made to the presence of any other deleterious material such as clay.

The ATEC report does not provide any particular information concerning the frequency and location of sampling for the above mentioned aggregate tests. Based on their findings, ATEC concluded that the aggregates could be used for structural concrete, provided a series of measures were taken, namely, pursuing additional investigations, or using low-alkali cements, adding pozzolans, or adding admixtures (suggested lithium hydroxide as an alternative, as well as water reducing admixtures) . ATEC also recommended that more research should be performed prior to designing trial mixes.

Compaction tests (AASHTO T-180-C) were run by All State Engineering and Testing Consultants, Inc. on samples taken at the above mentioned facility more recently (February 1994) . Maximum dry unit weights of 103.2 to 106.8 pcf and optimum moisture contents of 9.3% to 9. 5% were determined for mixtures of red and black cinder soils. The results are summarized in the following Table.

ALL STATE ENGINEERING AND TESTING CONSULTANTS, INC. (1994)

CONSOLIDATED INSTRUMENTATION FACILITY

Test Compaction (AASHTO T-180-C)

Material Red and Black Cinders

Maximum dry unit weight (pcf) 103.2-106.8

Optimum Moisture Content ( % ) 9.3-9.5

Froehling & Robertson, Inc. (F & R) performed an investigation in 1992 for the Power and Desalination Plant located north of the airfield (Referenced in Appendix A) . The exploration was aimed at defining bearing capacity properties of the soils and rocks. A total of sixteen borings were performed at the site. The depths

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Ascension Island Page 1.2 ranged from l4.5 feet to 24.5 feet. SPT tests and Rock Quality Designation (RQD) determinations were carried out in each hole.

RQD values were not included in the copy of the report sent to GCI.

Three (3) strata were defined: loose black and red cinders and ash; gray basaltic scoria; and gray basalt.

A visual evaluation of size and relative proportion of voids in recovered samples was performed. In general, void sizes ranged from 0.25 inch to l.75 inches, representing up to 80% of the total volume. No water table was encountered at the borings. Unconfined compression tests were performed on six (6) rock cores, including specimens with 40% or larger void volumes. Unconfined compression strength values ranged from 2,630 psi to l0,750 psi. Based on the Rock Mass Rating (RMR) (taking into account RQD, rock strength, ground water conditions and joint/fracture spacing) , F&R classified the materials as a 11 fair rock". The results are summarized as follows.

FROEHLING & ROBERTSON, INC. (l992)

POWER AND DESALINATION PLANT

Number of Borings 16

Depth (ft) l4.5-24.5

Ground Water Table Not encountered

Strata (a total of three) (l) Loose cinders

(2) Gray Basaltic ( 3) Gray Basalt and ash scoria

Rock Voids (basaltic scoria) Size varies from 0.25 to 1.75 inch, occupying up to 80% of the total volume

Rock Strength (psi) 2,630-l0,750

Rock Mass Rating (RMR) Fair Rock

It must be pointed out that the above-referenced· study did not include either chemical-petrographical analyses, or standard testing (abrasion, absorption, etc.) related to the suitability for concrete manufacturing.

Two compaction tests (ASTM D-698) were run by Engineering Consulting Services, Ltd. (ECS) on samples collected at the above referenced facility more recently (May 94) . Maximum dry unit weights of ll0.4 to l24.2 pcf and optimum moisture contents of 6.3% to 6.6% were determined for what appears to be a mixture of gray basalt fragments and red cinders. The results are summarized as follows.

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Ascension Island

A brief explanation of the aspects that deserve more attention in the next phase of the study follows. The presentation is based on the framework provided by Kosmatka and Panarese (1988) .

Grading

Grading influences relative aggregate proportions / cement and water requirements. It also affects workability 1 pumpability 1 economy 1 porosity 1 shrinkage and durability of concrete. Aspects such as workability and pumpability deserve special attention. Grading requirements for coarse aggregate are given in the attached Table 3.

Particle Shape and Surface Texture

These parameters exert a marked influence on the properties of freshly-mixed concrete / more than they do on the hardened concrete.

Rough-textured 1 angular particles (which may be the case of the Island aggregates) may require larger cement quantities to assure appropriate workability. The cement paste-aggregate may be stronger 1 compared to mixes with rounded smooth particles. This may be an advantage if high strength concrete is required. Larger angularity may lead to more pronounced abrasion during stocking and hauling operations.

Elongated shapes are to be avoided 1 as larger amounts of water (and therefore larger amounts of cement) are required to maintain workability/pumpability.

Unit Weight and Voids

Mortar requirements and mix design are affected by the unit weight and voids. Larger void volumes are to be expected due to the (expected) angularity of the particles at the Island.

Specific Gravity

This property influences mix design but is not used for aggregate grading. Nevertheless / aggregates with larger porosity may lead to concrete deterioration under freeze-thaw cycles. This situation is not applicable at the subject site.

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Ascension Island Page 1.5

Water Absorption

Large absorption values may· be expected if scoriaceous/cinder materials are considered. The tendency to absorb water plays a relevant role in their performance in concrete production 1 and must be prevented. Procedures such as soaking, sprinkling and vacuum soaking could be used to handle the problem .

Wetting and Drying Properties

Concrete under wetting/drying cycles may deteriorate depending on corresponding response of the aggregates to such phenomena. Clay lumps or any other types of material that degrade under repeated changes in moisture content are to be avoided. Current information about geotechnical properties of local weathered rocks is not available for any judgements about this issue. While no specific tests are available to determine this tendency / an experienced petrographer can often be of assisstance in determining the potential for distress.

Abrasion and Skid Resistance

Abrasion resistance is utilized as a general index of the quality of the aggregate. It is relevant if the concrete will be subjected to abrasion 1 say in floors or pavements. On the other hand 1 it provides information on possible deterioration of the aggregates during handling and mixing. As they degrade 1 fines are produced.

If so 1 more water is to be added to the mix 1 for example.

A maximum wear (expressed as the percent worn away during repeated impact, Los Angeles Abrasion test) of 50~ is usually specified as an acceptable limit.

Nevertheless, the specialized literature indicates that there is no clear correlation between actual concrete abrasion resistance and corresponding aggregate abrasion resistance. We recommend that abrasion tests be performed on the concrete.

Skid resistance in pavements is achieved by specifying that at least 25~ of the aggregates be siliceous.

Strength of the Aggregates

The strength of the aggregates does not generally influence normal weight concrete. Therefore / no specific testing is required routinely 1 except if high-strength mixes are needed.

Ascension Island

Resistance to Chemical Attack

Common chemical and corrosion attack may be produced by acidic solutions acid rain 1 bicarbonate solutions 1 sulfate solutions and organic acids. Corrosion may be a problem in structures built in water. Special measures such as coatings 1 reduced permeability 1 low water-cement ratios / low-to-moderate cement ratios and the addition of pozzolans or slag / may be used to circumvent the problem.

Deleterious Substances I Alkali Reactivity

As stated before 1 materials containing clay affect the behavior of concrete. Other harmful materials are organic impurities 1 silt 1 iron oxides (may cause stains) / coal 1 and lignite 1 among others.

The attached Table 4 presents a list of harmful materials.

Aggregates may contain substances that actually react with Portland cement, and may cause volume changes 1 interfere with hydration or give origin to harmful products. The attached Tables 4 & 5 present a list of such materials.

Previous studies / referenced in Appendix A1 indicate that the examined materials contain appreciable quantities of volcanic glass and cristobalite which may react with the cement. To the best of our knowledge 1 no specific research or testing 1 such as the mortar base test has been performed in the past in connection with this phenomenon or the other types of deleterious substances. Some of them 1 such as iron oxides (apparently occurring in the observed cinders) may deserve attention as well.

ENGINEERING EVALUATION

Preliminary Evaluation

Based on the available test results 1 a preliminary assessment of the island basaltic rock aggregates is summarized as follows:

PRELIMINARY ASSESSMENT OF THE ISLAND BASALTIC ROCK AGGREGATES

ITEM COMMENTS

Grading One series of tests indicate that material approximates ASTM C-33 requirements for a 57 size (ATEC study)

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PRELIMINARY ASSESSMENT OF THE ISLAND BASALTIC ROCK AGGREGATES

(CONT'D)

ITEM COMMENTS

Abrasion Complies with standards

Resistance to weathering No tests done yet (tests in sulfates)

Particle shape and surface Only qualitative assessment texture done so far

Bulk density Within typical range (75 to 110 pcf)

Absorption Larger than typical values for coarse aggregates

Aggregate constituents May contain alkali-reactive componentsi Other harmful materials not addressed yet

Resistance to alkali No specific testing done yet reactivity

Supplemental Evaluation

A more detailed evaluation of the geotechnical/geomorphologic features of selected potential borrow areas and access corridors seems in order. Aspects such as structural features at outcrops (weathering profile, joints), existing slope stability conditions and surface drainage would be addressed. This task could be aided by aerial photograph(s) interpretation.

A sampling program would then be planned and pursued, via test pits and borings. The laboratory testing program would involve the items covered in Tables 2 and 4.

All tests, excluding petrographical examinations, could be carried out in an on-site laboratory that would be transported to the Island. Rock cores or samples for detailed examinations would be shipped to our laboratory. Special attention would be given to the following items: mix design (gradation, absorption, particle shape and texture) in connection with concrete workability and pumpability) ; measures to handle high-porosity aggregates; presence of potentially alkali-reactive materials; strength of in-situ rock and blocks/bombs, to assess material crushing properties.

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In-situ seismic (reflection or refraction) profiling could be done at selected potential borrow areas. The results could be used to assess the rippability of materials (use of mechanical equipment large bulldozers or backhoes or dynamite) on a larger scale basis.

The design of the quarrying system would follow. Disposition of the pits, heights and inclination of the walls, depth of required stripping, storage of refuse, environmental issues (refuse handling, drainage during rains 1 erosion control systems and future reclamation) .

Mining Operations

On-Going Rock Mining Operations

Mining operations in the rock quarry and surface strip mining (antenna field) areas have been carried out using bulldozers 1 front end blade rippers and hydraulic hammers. Large blocks of rock are removed and then stockpiled and fractured into l2 to l5-inch diameter blocks for transportation to the crusher.

The l2 to l5-inch size blocks are crushed in a primary crusher into 4 to 6-inch rocks which are then conveyed to a second crusher for final processing.

Exploitation of the black and red cinder quarry areas of removal/stripping of the material with backhoes.

end loader is then used to stockpile and load the into dump trucks for transportation.

consists A front material

The list of U.S. Government operational equipment on the Island is as follows:

OPERATIONAL EQUIPMENT

EQUIPMENT DESCRIPTION/REMARKS

Crane 60 Ton 1 Grove

Dozer Flat Allis

Road Grader 12' Blade

Truck Tractor l0-l5 Ton

Asphalt Distributor 800 gallon capacity

Concrete Batch Plant 5 cy. capacity

Concrete Mixer Truck 10 cy. capacity

Road Roller Towed

Road Roller Steel Wheels, 5-8 Ton

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Ascension Island

OPERATIONAL EQUIPMENT (CONT'D)

EQUIPMENT DESCRIPTION/REMARKS

Aggregate Spreader ---

Distributor Water 1500 gallons

Crane 90 Ton, Grove

Hi-Ranger 65 feet

Lowbed Semi-Trailer 20 Ton capacity

Concrete Mixer 16 cu. ft.

Concrete Mixer 6 cu. ft.

Forklift 15,000 lb capacity

Rotary Sweeper Towed

Crane 7.5 Ton, Lorain

Concrete Pump ---

Tracker Excavator ---

Crushers 1sn-2on limit size, 15n screen

Crusher 4n -6n: limit size

Hammer 160 Ton

4 Barrel Single Shank Ripper ---

Dump Trucks 5 and 10 Ton capacity

Backhoes ---

Alternate Rock Mining Procedures

As indicated earlier in this report, trachyte and rhyolite flows (central and eastern parts of the island) and basaltic flows are found at Ascension Island. Dynamite could be utilized to produce large fragments of rock. However, its use is not favored due to the difficulties involved in transporting and storing the explosives. Other alternatives for mechanical ripping and fragmentation include:

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Mechanical Ripping: Rippers have been used to rip strong materials in various parts of the world. Igneous rocks may be at that 11 threshold 11 where rippability may become an issue .

Basic factors that affect the performance of the method include resistance of the rock, degree of weathering and the presence of joints, bedding, laminations or foliation.

Some ways have been devised that may try to encompass the rock mass features. Two of them may be applicable to the situation at the Island.

The so-called Rock Mass Rating (RMR) system and the use of sonic velocity. Current information on the geotechnical properties of the island rock seem to be scarce, to the best of our knowledge. According to Abdullatif and Cruden (1983), the RMR system may give a guidance about rippability. They conclude that rock masses with an RMR smaller than 60 may be rippablei if RMR is larger than 60, blasting may be required.

The study done by F&R at the Power and Desalination Plant site indicates an RMR of 24 to 60. These results, although strictly applicable to the referenced site, may indicate that mechanical ripping may be feasible in some parts only.

Another method is based on the propagation velocity of waves (compression or P-waves) in the rock mass. No information on seismic geophysical testing, at the subject site, is available to GCI at this time. This type of investigation does not pose any special difficulties and can be readily performed by specialized companies.

A more comprehensive geological/geotechnical study and some field trials are to be performed to reach definite conclusions and recommendations on this matter. It must be kept in mind that the composition and characteristics of volcanic rocks at the island differ from one area to another. Pre-blasting may be required to prepare the terrain prior to ripping.

Fragmentation: Fragmentation could be pursued by means of the so-called pneumatic rock breakers. They are usually hand operated or boom-mounted pneumatic picks, that can be used even in strong rocks. This method is suited to situations where ripping is unfeasible, when blasting may be deemed unacceptable or when the availability or handling of explosives becomes a problem.

Further fragmentation could be accomplished using the methods already described (hammers, picks, drop balls, grid rollers).

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Cuts in lava flows may encounter some features that deserve some care. This includes the presence of thin veneers of buried ashes or cinders. This material could be weaker and may induce landslides. The construction of a bench may be in order to accommodate eventual slumps or the installation of retaining structures.

Occurrence of joints oriented in an unfavorable condition may affect the mining procedures selected. Their presence may lead to changes in the orientation of cuts or the need for stabilizing procedures (anchoring, benching, etc.).

The fragmentation of large blocks poses a problem. Existing methods to break the blocks into smaller pieces for transportation to the crusher include:

Mudcapping: Heavy charges of explosive (highest velocity type) are set on top of the block and covered with mud.

Large amounts of dynamite and wastes are involved.

Snakehole: The explosive is set in a hole dug underneath the block. There is less waste compared to the previous technique (Mudcapping) .

Blockhole: A hole is drilled in the block and a small charge of explosive is set at the bottom. This method is somewhat risky as rock pieces may be thrown long distances.

Bristar: More recently / new products have been developed that induce fragmentation as they swell. As an example, we can refer to one called Bristar, developed by Onoda Cement Company / Ltd. (Japan) . The powdery product is mixed with the recommended amount of water and is poured into pre drilled holes in the rock (outcrop or large blocks) .

Expansive stresses in excess of 600 tsf develop as the product hydrates. There is a variety of mixes to be used depending on working temperature. A series of recommendations on hole diameter (typically 1/2 11 to 2 11

) and hole separations (typically 2 to 3 feet) are provided by the manufacturer.

In our experience, this type of system is worth trying.

However, special care is required in following the directions of the manufacturer.

Drop Ball: A drop ball (about 0. 5 to 4 Tons in weight) handled by a crane is dropped at the area mined. Pieces of rock may be expelled over considerable distances, thus making the operation risky. A light portable pile driver, installed on a crane or loader and fitted with a demolition head may also be used.

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Pneumatic rock breakage: The fragmentation could also be pursued by means of the so-called pneumatic rock breakers.

They are usually hand-operated or boom-mounted pneumatic picks, that can be used even in strong rocks. The scheme is suited to situations where blasting may be deemed unacceptable or where the availability or handling of explosives becomes a problem.

Heavy ballasted grid rollers: The surface of the drum is made of steel sections. This type of equipment has been used to crush loose rock 1 including basalt. The material is first ripped/blasted, then it is hauled and spread on a flat resistant surface.

Wedge insertion: A wedge is driven in a pre-drilled hole.

The operation is time-consuming. Mostly used in braking dimension stone and masonry.

On-going Cinder Mining Operations

Black and red (oxidized) cinders appear at the ground surface.

They may be buried as thin veneers within lava flows, also.

Previous geotechnical studies and existing experience at the site indicate that these materials are rippable. Ripping is performed to loosen the material for further excavation. The equipment is commonly installed on a tractor or a bulldozer.

It may consist of one or more teeth (called shanks) which can be straight .or curved. Straight shanks may be more appropriate in tight laminated materials / whereas curved shanks may be more suitable for porous materials 1 which seems to fit the situation at hand.

The directions of ripping depend on the extent / depth and shape of the area to be exploited. The orientation of the joints (if applicable) in the deposit must be taken into consideration as well.

Some basic rules about the procedures can be summarized as follows:

Ripping should proceed in the same direction that scrapers or the equipment to excavate will load/push the material.

Operating downhill is best. On occasion 1 doing it uphill is advisable 1 especially if slabby materials are present.

The area may be covered in two different directions (cross ripping) under difficult circumstances.

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RECOMMENDATIONS FOR FUTURE EXPLOITATION

General

As observed in our visit, exploitation of cinders is being performed in a large area, to a depth of about 30 feet. We recommend that the following aspects be taken into account, should the pits go larger or deeper:

The inclination of the cuts should not exceed 35° to the horizontal.

Benching is not recommended, because the porosity and heterogeneity of the materials might trigger or eventually lead to local instability problems.

It is known that strong occasional rains occur at the Island. Any runoff over the slopes is to be prevented.

Ditches could be dug behind the top of the hanging walls, at about 5 feet, to divert the water flow. Such ditches could be lined with a geomembrane (short term) and eventually plain concrete (long term) . Outlets and discharges (made of ash/cinder-cement mix or via gabions) are to be set at selected sites. It may be easier and more convenient to define their locations in the field.

The exploited materials may be potentially abrasive, especially those belonging to more siliceous formations (trachyte and rhyolite) that exist in the central and mid-eastern parts…