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Author Archives: Thrasher NC

The Role of Land Surveyors and Civil Engineers in Rebuilding and Recovery After a Natural Disaster

The Thrasher Group North Carolina is proud of how our team came together to support communities impacted by the devastation caused by the natural disaster Hurricane Helene in the Fall of 2024.

While employees volunteering and collecting essential supplies helped to meet immediate needs, we know our largest contribution will happen over time – as we serve in our roles as land surveyors, engineers, and construction managers.

Western NC faces a long road ahead. Full recovery, including restoring and rebuilding critical infrastructure like utilities and roads will likely take years. Below are some ways that land surveyors and engineers play an essential role in long-term recovery after a natural disaster.

Funding and Compliance for Natural Disaster Recovery

Securing funding (a natural disaster means unexpected and unbudgeted costs) and ensuring compliance with local, state and federal regulations adds another level of complexity to rebuilding efforts.

FEMA’s public assistance program, for example, requires communities to meet specific criteria such as being located in a declared disaster area and proving that they’ve incurred eligible costs. Qualifying for this program requires detailed documentation with which seasoned surveying and engineering teams can support.

Additionally, plans for rebuilding structures must meet detailed requirements, for example, specific elevations (to reduce future flood damage risk) or floodproofing measures like flood vents or watertight doors. Local building codes and zoning ordinances also require permits and inspections to ensure compliance with safety standards. Even new infrastructure and utilities systems must adhere to design standards, quality control and safety regulations

Experienced surveyors and engineers should be well-equipped to assess damages and plan compliant reconstruction efforts, while also helping communities navigate FEMA and state funding processes.

Land Surveying for Infrastructure and Environmental Recovery

Land surveyors play a critical role in the aftermath of hurricanes and other natural disasters. Surveyors help to assess the extent of damage to land and property and identify changes in land elevation and topography. They are also key in re-establishing property lines and boundaries, especially when natural disasters move or obscure original boundary markers. Land surveyors also conduct infrastructure surveys, which map and measure roads, bridges, pipelines, and power lines. Surveys also provide the foundational data needed to make informed decisions about environmental recovery, protecting water resources and stabilizing the soil.

By providing critical baseline data on infrastructure and land conditions after a natural event, surveyors empower communities to rebuild stronger. This is especially important after devastating events like Hurricane Helene, when the ground itself may have been compromised from flooding and a large number of structures impacted. Timely and accurate surveying work is key to help prioritize and guide rebuilding efforts in a way that will prevent future risk from natural disasters.

Structural Engineering for Rebuilding and Long-Term Safety

While land surveyors help to ensure rebuilding occurs on stable ground and within the correct boundaries, structural engineers ensure that the design of new or rebuilt structures and buildings are safe, stable and durable.

In the immediate aftermath of a natural disaster, structural engineers are on the front lines assessing the structural integrity of impacted structures and documenting damaged and collapsed buildings. These assessments tell authorities whether structures are safe to inhabit as is or need reinforcement before its occupants or residents can return. In extreme cases, structures may be condemned and slated for demolition.

From this documentation, engineers can also begin to develop structure repair plans and strengthening measures, designing new structures to withstand future disasters. For example, engineers may suggest incorporating features like retaining walls, drainage systems and flood barriers to mitigate future risks like landslides and flooding.

Transportation and Water Engineering in the Aftermath of a Disaster

Civil engineers specializing in transportation and water engineering have a special role to play in the immediate aftermath of a disaster. They are key in providing clear and timely information to local authorities about water quality and transportation safety.

Transportation engineers work to assess damage to highways, roads, bridges, parking decks and sidewalks. Authorities use this information to communicate which are or are not passable and safe. Water engineers perform water quality testing, which local authorities use to decide whether they should issue public health notices for contaminated drinking water. If a notice is issued, citizens will need immediate access to clean water, linking back to the need for passable roads to deliver supplies. (Even in the event of a boil water advisory, bottled water is ideal as boiling water only kills pathogens, but can’t remove many other contaminants.)

Restoring access to roads and bridges (so that citizens can get to safety and supplies can flow freely) and critical resources like water will always be most pressing immediately following a catastrophic natural event. Information provided by engineers informs prioritization of areas that require immediate attention based on access to emergency services, critical infrastructure and population density.

Once water and transportation engineers play their more immediate roles, they can then get to work on long-term infrastructure and utilities improvement. These civil engineers create the plans for rebuilding transportation and utilities infrastructure, all while taking into account factors like climate change, future land use and patterns.

They work to design rebuilt infrastructure for increased resilience to future natural disasters, for example, elevated roads or water treatment facilities, flood-resistant  bridge designs and early warning systems. Many civil engineering firms can also provide construction management services and oversight, to ensure that the new infrastructure built adheres to the original plans provided.

Does your community need support?
Whether it’s restoring critical infrastructure like roads and bridges or rebuilding essential utilities, Thrasher NC is committed to tailoring solutions to each community’s unique needs. Contact us today and we’d be happy to help learn your community’s story and assist with current surveying, engineering and construction management needs.


Essential Concrete Strength Testing Methods

Concrete is a critical structural element, and its strength directly impacts a building’s safety. But how do we ensure it meets the demands placed upon it? Concrete strength testing ensures a concrete mix meets design specifications for its intended load-bearing capacity, to ensure the structure’s stability and prevent potential failures.

Concrete strength is most commonly measured by testing its compressive strength, which measures its ability to withstand forces pushing it inwards and together. This article reviews methods for testing concrete strength, both in the controlled environment of a lab and on-site in the field. We’ll also explore preparation methods used for the concrete test specimens and other concrete tests indirectly related to strength.


Q: What units are used when concrete compressive strength is measured?


Concrete being strength tested in a lab

Lab Testing: Strength Testing & Related Tests During Planning and Pre-Construction

Lab testing a calculation of concrete strength under controlled conditions. It is typically used for initial mix design and strength evaluation during planning and pre-construction or to help with batching quality control.

Note: While lab samples can be useful, they might not exactly replicate the actual curing conditions on the construction site. Enter the need for field testing for verifying in-situ strength, which will be discussed later in this article.

Lab Concrete Strength Cylinder Test (ASTM C39): This lab test measures a concrete cylinder’s ability to withstand a compressive load until failure and is the primary method used by engineers for determining concrete strength. Cylinders are cast from the fresh concrete mix and cured under controlled temperature and humidity conditions which mimic the actual construction site environment. After a specified period (usually 7 or 28 days), the cylinders are crushed in a hydraulic press. This machine applies a compressive force on the ends of the cylinder, gradually increasing the pressure, until the cylinder cracks or breaks.

The maximum load it can bear is then recorded. The load is divided by the cylinder’s cross-sectional area to obtain the compressive strength. This compressive strength value becomes a benchmark for the concrete’s overall strength.

The desired compressive strength will depend on the intended use for the concrete. Sidewalk and driveway projects, for example, may require a lower psi than commercial buildings and warehouses.

Field cylinders may also undergo the ASTM C39 test (see: Making and Curing Test Specimens (ASTM C31) below for more detail). Field cylinders evaluate the concrete’s actual strength “in-situ” within the structure, while lab cylinders assess the mix design’s potential under controlled conditions.

Unbonded Capping of Concrete Cylinders (ASTM C1231):

In concrete strength testing, unbonded capping is an alternative method for preparing the ends of cylindrical concrete specimens so that they are flat. For an accurate test, the top and bottom faces of the cylinder must be perpendicular to its axis. Uneven load-bearing surfaces can introduce errors in the test results.

Unbonded capping uses a flexible pad, typically neoprene or rubber, instead of a bonded capping material like sulfur mortar or neat cement paste. The pad is placed on each end of the concrete cylinder and steel retainer rings hold the pads securely in place to create a smooth, flat surface.

Unbonded caps are quicker to apply and remove (vs. grinding or cutting uneven ends or bonded capping) for faster preparation of specimens before each test The pads may be reused up to 100 times, reducing waste and cost (vs. single-use bonded caps).

However, unbonded capping cannot be used in every case. ASTM C1231 outlines limitations for using unbonded caps. They are generally not suitable for very low (below 10 MPa or 1500 psi) or very high strength (above 80 MPa or 12000 psi) concrete. Unbonded caps are suitable for concrete with minor imperfections on the ends, up to 5 mm (around 3/16 inches). For larger deviations, grinding or cutting the cylinder ends might be necessary before testing.

Field Testing: Assessing In-Situ Strength

While lab testing provides valuable insights for planning and pre-construction, construction also requires assessing the strength of concrete after it has been poured and cured on-site in actual field conditions. Field testing is key for investigating potential concrete strength issues in existing structures – especially when quick confirmation of adequate strength is needed for construction progress.

Below are a few key strength-related concrete field testing methods and processes:

Slump Test (ASTM C143): The Slump Test is a quick test that measures the consistency and workability of fresh (unhardened) cement concrete, which impacts its compaction and ultimately, its strength. Concrete with a higher slump may be easier to place but can lead to trapped air and reduced strength. The Slump Test is a valuable tool for concrete quality control in the field, ensuring the correct consistency (not too wet or too dry) and cohesion (the ingredients are holding together well).

To conduct the Slump Test, a cone-shaped mold is filled with concrete in layers and rodded to remove air bubbles. The mold is lifted straight up, and the slump is the distance that the center of the concrete settles. This indicates how easily the concrete will flow and fill forms, with a moderate slump (between 1/2 inch and 9 inches) being ideal for most applications.

Sampling of Freshly Mixed Concrete (ASTM C172): Obtaining a representative sample of fresh concrete ensures accurate concrete strength testing. Following ASTM C172 ensures a well-mixed composite sample that accurately reflects the overall properties of the concrete batch for reliable strength testing. Samples are taken from the middle portion of the concrete batch, avoiding the first and last portions that may not be well mixed.

For portable drum mixers and mixer trucks, sampling occurs during discharge, when a container is inserted into the stream, or the concrete flow is diverted into a container during discharge. For paving mixers, samples are collected from five locations after the entire contents of the paving mixer are discharged onto the ground where the concrete will be placed.

Regardless of the mixer type, it’s crucial to collect the sample within the specified timeframe (usually 15 minutes after obtaining the first portion) to ensure the properties haven’t changed significantly.

Making and Curing Test Specimens (ASTM C31): ASTM C31 outlines the process for making and curing cylindrical or beam-shaped concrete test specimens in the field. Fresh concrete is obtained following ASTM C172 and placed in molds in layers. Each layer is rodded to eliminate air bubbles, and the top is smoothed. The molds are covered to prevent moisture loss and kept at a specific temperature range for an initial curing period. Then, the specimens are demolded and submerged in water or a limewater solution for final curing until testing, typically at 28 days. This ensures the concrete reaches a controlled and standardized strength for accurate compressive strength test results.

Temperature of Concrete (ASTM C1064): ASTM C1064 is a standard test method for determining the temperature of freshly mixed concrete at the time of placement. It outlines how to measure the temperature using a specific type of thermometer that can be inserted into the concrete. The field concrete test ensures the concrete is within a proper temperature range (typically between 30°F and 120°F or 0°C and 50°C). This is important for concrete strength because extreme temperatures can affect the setting time, workability, and thus, the ultimate strength of the concrete.

Unit Weight (ASTM C138): ASTM C138 is a test method to determine the unit weight (also sometimes referred to as density) of fresh concrete. Unit weight is important for estimating yield of concrete from a mix design (knowing the unit weight allows engineers to calculate the actual volume of the resulting concrete from the ingredients) and quality control (unit weight variations can indicate potential issues with the mix proportions, mixing process or presence of air bubbles).

The test involves filling a specific mold with the fresh concrete and compacting it according to the standard. The weight of the filled mold is then measured, and dividing this weight by the known volume of the mold gives the unit weight of the concrete.

This test has an indirect relationship to concrete strength. Higher unit weight typically indicates a denser concrete mix with fewer air pockets, which usually means a higher strength. However, it’s not a standalone measure of strength. For example, a concrete mix with a higher unit weight due to the amount of heavy aggregate might not necessarily be stronger than a mix with a lower unit weight that has a more optional mix design.

Air Content by  Pressure Method (ASTM C231): The Air Content by Pressure Method test measures the volume of air entrapped within the concrete mix and is used for concrete made with relatively dense aggregate particles, excluding internal air voids within the aggregates themselves. The pressure method test uses a special apparatus called an air meter, which is filled with a concrete sample and water. The air meter bucket rim is cleaned and the top section is placed, after which sealed water is introduced through one of either petcocks until all air bubbles dissipate, then the petcocks are closed. Air pressure is applied, and the change in volume of the trapped air is measured. Maintaining the desired air content is crucial for ensuring concrete durability, workability, and achieving the target strength. Too little air can lead to freeze-thaw damage, while too much air can reduce strength.

Air Content by Volumetric Method (ASTM C173): The Air Content by  Volumetric Method outlined in ASTM C173 is a test to measure the air trapped within fresh concrete. This test helps ensure the concrete has the proper amount of air for workability and freeze-thaw resistance. Its value lies in its ability to accurately measure air content in concrete where the air content by pressure method might struggle, such as lightweight concrete and those with highly porous aggregates. Generally, higher air content leads to lower strength, however it is not a direct measure of concrete strength.

For this test, concrete is placed in the meter bucket in two layers, rodded and sides tapped for each layer. The bucket rim is cleaned, and the graduated neck is placed on the bucket and clamped for a tight seal. The funnel is then placed in the neck and a small amount of water is added before introducing 2 pt of 70% isopropyl alcohol, then the remaining water is added up to the 0 mark. Then the top is added and sealed into place.

The meter is then shaken and rolled to release air bubbles. The water level in the neck rises due to the displaced air, and this change in level indicates the air content as a percentage of the total concrete volume. This test helps ensure the concrete has the proper amount of air for workability and freeze-thaw resistance.

Ready to begin testing?

By employing a combination of these tests, engineers gain a comprehensive understanding of concrete’s properties, ensuring a safe and structurally sound construction project. Need concrete strength testing services or other concrete construction materials testing?  Contact The Thrasher Group NC about our AASHTO and CCRL accredited test lab and services.


Past to Present: Building Legacy at the Heart of Gaston County

The Thrasher Group North Carolina’s Gastonia office is located in what historically was known as the Loray Mill, and later Firestone Cotton Mill. Loray Mill — also nicknamed “Million Dollar Mill” — was one of the largest textile facilities in the South. The building continues it’s legacy of making Gaston County an economic hub still to this day.

At its peak in the early 1900s, Loray Mill employed over 750 workers and was a technological and structural powerhouse. Tying in architectural and structural engineering from New England, Loray Mill’s facilities were equipped with firewall partitions and fire doors to the interior to limit the spread of fire, all while maintaining aesthetic Italianate details with arched windows and a pyramidal roof on the exterior of the building. Further, the mill stood apart in the South because of its experimental steam power source and air conditioning systems.

The mill closed its doors in 1993, and while it no longer produces textiles, the mill still presents itself as an impressionable space for the community. With modernized housing and office spaces, including Thrasher NC, the mill provides the Gaston community with a collaborative space for economic advancement while preserving the rich local history.

The Thrasher Group North Carolina strives to continue Loray Mill’s legacy of being at the heart of the community by passionately supporting our municipalities and neighborhoods, providing local jobs, and serving the area’s infrastructure needs. 

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Meeting Complex Land Survey Needs for Proposed Lithium Mine Re-Opening

Project Location: Kings Mountain, NC

Site of Albemarle Corporation’s former lithium mine in Kings Mountain

Background:

Kings Mountain, North Carolina, is home to a former lithium mine that has sat dormant for nearly four decades. The site sits atop a deposit that could help meet the growing demand for the lithium needed to support the electric vehicle supply chain and clean energy production in the United States.

Demand for lithium is not driven by the EV market alone. The lithium concentrate that can be derived from the proposed mine is needed to power everything from consumer electronics to life-saving medical devices. There are also national security interests that factor into this potential domestic source of lithium, for example, lithium-ion batteries are used by the U.S. Department of Defense for satellites.   

Overview:

When Albemarle Corporation, a global leader in the specialty chemicals industry, began to explore resuming mining at the Kings Mountain site, it contacted The Thrasher Group North Carolina to help with surveying the original site footprint. The company was pleasantly surprised to find an experienced local contractor with a working knowledge of the community to meet all of its site surveying needs for pre-feasibility studies.

Today, the Albemarle continues to use Thrasher NC’s land surveying services as it prepares for advancing to the permitting process and other necessary pre-construction steps.

Project Goals:

  • Original survey of the 500+ acre legacy parcel and additional surveying services as Albemarle expands the footprint via 100+ parcel acquisitions for buffers zones
  • Identify and highlight improvements, easements, rights-of-way and other important survey information that could impact the feasibility of mining operations
  • Survey the surrounding buffer parcels that Albemarle would need to acquire in order to meet buffer area requirements

Land Surveying Services Provided: 

  • Photogrammetry surveying services
  • Geo-spatial surveying services
  • GNSS/GPS surveying services
  • Conventional surveying services

Training Processes Completed:

  • Completed extensive Mine Safety & Health Administration (MSHA) Training
  • Completed site-specific Albemarle-required training and certification
  • Vetted via 3-month ISNetworld supplier certification process 

Project Approach:

The original land survey of the original footprint was started in 2018. Today, Thrasher NC is in the process of a phased approach with surveying services for additional properties surrounding the original site, anticipating completion of the overall surveying project in 2025.

Project Challenges:

  • Project Size: The entire Kings Mountain site, which also includes a Lithium Conversion Facility and the companies Global Technology Center offices, encompasses >1500 acres. Finding a partner that could keep pace with Albemarle’s need for the original parcel and buffer area acquisition surveying processes was key.
  • Legal & Environmental Communication:  Thrasher NC’s surveying professionals sit in on weekly coordination meetings with attorneys, land agents, and other key project stakeholders to ensure the team is in the loop and available if additional site questions arise.

Project Outcomes:

The Thrasher Group North Carolina has provided Albemarle with all the necessary site surveying services it has needed for the Kings Mountain Lithium Mine in a timely manner.

Since site surveying was a prerequisite for Albemarle to move the project forward through complex pre-feasibility studies, permitting and pre-construction planning, the Thrasher NC team’s timely delivery also allowed Albemarle to stay on track with its own timelines.

There is a water treatment plant on the current parcel, and if needs arise in the future, The Thrasher Group North Carolina can also provide water resources engineering due to its multidisciplinary offerings.