MIC-resistant Concrete Admixture and Spincasting Rescue Sewer Manholes. Laredo, Texas, founded in 1755, is a particularly old city. With a population of 250,000 it’s also one of Texas’ biggest cities, and is currently the fastest growing. This growth puts significant stress on the city’s aging—in places antique—sewer infrastructure. “We have 700 miles of pipe in our sanitary sewer network, half clay and half PVC,” says Angel Leon.