One major refinery located in the Southwest faced three major high-priority civil infrastructure projects scheduled concurrently for a Delayed Coking Unit Turnaround (T/A). The success of this challenging project depended on Structural Preservation Systems' (SPS) innovative project construction phasing; the combination of precast, cast-in-place and post-tensioned concrete construction technologies; and the incorporation of other extremely durable construction materials in the creation of a process coined the "T/A Civil Approach" (TCA).
In the refinery's DCU, a 64-year-old furnace foundation wall, as well as the coke drum support structure and the coker railroad sluiceway trench were subject to extreme environmental service conditions, including high temperatures (212 to 1,200 degrees Fahrenheit), aggressive chemical attack, process water erosion, railroad car impact and thermal shock. SPS team members noted that deterioration of the structures included concrete cracking, delamination, spalling and exposed corroding reinforcing steel bars; corroded vessel anchor bolts and structural steel members; failed foundation walls and sluiceway trench water nozzles; and warped railroad rails. Further, in the vicious cycle of repairing the repairs, those areas having undergone concrete repair commonly experienced failure due to inappropriate repair design, repair material selection, surface preparation and repair installation.
Mechanical properties revealed via laboratory testing demonstrated that the structure could accept and integrate new concrete repair materials. The use of high-quality, shrinkage-compensating repair concrete and high-capacity mechanical anchors placed at grid intervals, in addition to the augmentation of deteriorated reinforcing steel bars, was identified and selected as the optimal repair solution. Although extensive deterioration existed, enough competent concrete material remained that structural support shoring was not required, and repairs could be performed in phases without compromising their durability. Repairs made to the subject structure had to be performed concurrently with multiple trades, addressing numerous electro-mechanical process repairs and/or upgrades. As such, an intricate plan was devised and orchestrated by SPS, providing each of the contracting entities a position on the T/A schedule to complete their respective assignments.
High priority focus was placed on all three civil repair projects, with repair program provisions, including work crew specialization, work area protection and tangible production rates, updated in real time, with the critical path schedule updated accordingly. A team of concrete repair professionals including SPS was assembled specifically to address the many sluiceway trench challenges, each member bringing to the team unique expertise in materials science, structural engineering and construction management. To address these many challenges, SPS developed a repair concept that incorporated materials and production techniques from the refractory, transportation and commercial market sectors. This approach involved wire-line sawcutting for the demolition of massive reinforced concrete; thermal shock-, abrasion- and chemical-resistant materials for construction; precast concrete segmental construction; post-tensioning anchorage and fastening; waterproofing membrane systems; and quick-setting cementitious backfill.
The sidewalls and integral rail supports constituted the largest time restraint for re-establishing the sluiceway. As such, the team opted to use commercially available, conventionally reinforced precasting technology, integrated with high-quality, refractory-grade, stainless steel fiber-reinforced calcium aluminate cement concrete, to prefabricate the trench sidewalls. This hybrid technology addressed heat and chemical concerns while enhancing strength and abrasion resistance.
Yet another challenge was the task of making precast a viable alternative to cast-in-place construction. Specifically, the precast segments had to be symmetrical enough to reuse standard form molds, large enough to limit the total number of segments and reduce the number of construction joints, light enough for light cranes to handle during transportation and setting, yet massive enough to support the weight of coke-product-loaded hopper rail cars. A suitable compromise involved taking the approximately 200-foot-long trench and dividing it into six-foot lengths. Each independently reinforced segment was evaluated with shipping load weight and size restrictions, dictating that only the sidewalls could be economically precast and transported to the site. The resulting challenge of "fixing" the segments to the trench base was met by incorporating post-tensioning (PT) anchorage assemblies into a competent cast-in-place concrete base slab. Essentially, each precast segment was "bolted" to the cast-in-place base slab, where a torque was applied to the top of the PT anchor, forcing the precast segment down with a large permanent compressive force. With the major pieces of the design puzzle in place, additional details such as joint grouting, reworking the washdown system, waterproofing and backfilling were detailed and implemented.
Implementing the TCA model for the civil infrastructure repairs at this particular refinery proved an effective tool for developing and executing a successful overall repair program. The challenge of completing three major civil repair projects simultaneously demanded critical thinking in a compressed time frame. Innovation was a key element, as some conditions were unforeseen, such as buried utilities, weather, railroad rail transitions and equipment breakdown. SPS' knowledge, growth and dedication provided outstanding restoration work products that were delivered under budget and ahead of the critical path schedule.