London sits at roughly 250 metres above sea level, straddling the Thames River valley through a landscape shaped by glaciation. That elevation might not sound dramatic, but it comes with silty clay tills and pockets of glacial outwash that complicate flexible pavement design more than most contractors expect. The real challenge isn’t the asphalt mix itself — it’s what happens underneath during a freeze-thaw cycle. When November rain saturates the subgrade and January drops to minus 15, the pavement structure has to resist heave, thaw weakening, and the kind of fatigue cracking that shows up three springs later. Our approach ties structural number calculations directly to Ontario’s seasonal modulus variation, not just a textbook curve. Before finalizing the granular base thickness, many projects benefit from a CBR test to anchor the resilient modulus assumptions in actual site conditions rather than generic tables.
In London Ontario, the difference between a 15-year and a 25-year flexible pavement is rarely the asphalt — it’s whether the base course was designed for April’s saturated modulus, not August’s dry one.
Our approach and scope
Site-specific factors
A cold snap after a wet December can undo years of pavement life in a single season. London’s winter oscillates around the freezing point far more often than northern Ontario, which means the number of freeze-thaw cycles per year — often 40 to 60 — drives deterioration faster than extreme cold alone. The risk isn’t just potholes; it’s the progressive loss of subgrade support under the wheel path, invisible until the deflection basin deepens. A 2021 condition survey by the City noted that collector roads on silt till subgrades showed terminal roughness five to seven years ahead of design life when edge drains were omitted. Our risk assessment for flexible pavement design always isolates the spring-thaw window, calculating modulus recovery lag and specifying staged opening restrictions for heavy vehicles during March and early April.
Applicable standards
AASHTO Guide for Design of Pavement Structures (1993) with MTO supplemental mechanistic checks, OPSS 1010 — Material Specification for Aggregates — Base, Subbase, Select Subgrade, and Backfill Material, CSA A23.3 — Design of Concrete Structures (for rigid pavement tie-in detailing), ASTM D1883 — Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils, MTO Pavement Design and Rehabilitation Manual (2013, with regional London climate adjustments)
Other technical services
Mechanistic-Empirical Pavement Design
Full structural design for new subdivisions, collector roads, and commercial parking areas using AASHTO 93 with MTO regional calibration, including seasonal modulus input, ESAL projection, and terminal serviceability modelling.
Forensic Pavement Evaluation
Falling weight deflectometer (FWD) testing and back-calculation of layer moduli on existing roads showing premature distress, with root-cause analysis linking cracking patterns to subgrade conditions or drainage failures.
Typical parameters
Quick answers
What’s the typical cost range for a flexible pavement design package in London Ontario?
For a standard subdivision collector road or mid-size commercial parking lot, the combined geotechnical investigation and flexible pavement design runs between CA$2,300 and CA$7,320 depending on the number of boreholes, the extent of laboratory resilient modulus testing, and whether FWD verification is required. Projects with complex drainage or bridge approaches fall at the higher end.
How does the London climate affect the design life of flexible pavements?
London sees around 40 to 60 freeze-thaw cycles annually, far more than northern Ontario. Each cycle temporarily reduces subgrade modulus by 30 to 60 percent during the thaw window, concentrating fatigue damage. Our designs account for this by modelling a reduced effective modulus for March and April, which increases the required structural number by 10 to 20 percent compared to designs that only use a single summer modulus value.
Which asphalt binder grade is specified for London’s temperature range?
We specify Performance Graded PG 58-34 for the surface course and PG 52-34 for the binder course in most London applications. The low-temperature grade of -34°C covers the coldest recorded air temperatures in the region, while the high-temperature grade of 58°C handles the occasional July heat wave without rutting. For high-stress intersections, we may step up to PG 64-34 in the top lift.