In the foamed-concrete-backfilled-gas-pipeline project, the fluidity of foamed concrete has a great impact on the construction quality. This research studied the fluidity of foamed concrete through laboratory tests. By changing the water–cement ratio, admixtures, additives, foaming-agent content and other test parameters, foamed concrete with different fluidities was prepared, and the effects of the above parameters on the fluidity of foamed concrete were analyzed. At the same time, the construction equipment was improved in the three steps of transportation, production and pouring. The results show the factors affecting the fluidity of foamed concrete are, in order of importance, foaming-agent content > water–cement ratio > water-reducer content > admixture content. According to the orthogonal-test results, the control scheme meeting the fluidity requirements of the actual engineering project had gains as follows: the water–cement-ratio range from 0.5 to 0.6, the amount of admixture from 35% to 40%, the water-reducer content at 1% and the foaming-agent content from 3% to 3.5% so as to ensure the automatic leveling of foamed concrete under the best flow state.

Purpose: Definition of the most effective methods and components for strengthening weak Yoldian clays used in the creation of transport routes in the North regions. Methods: The definition of the main physical-mechanical characteristics of clay soil was carried out in accordance with the requirements: of GOST (Russia State Standard) 12536—2014 “Soils. Methods for laboratory determination of granulometric (grain) and microaggregate composition”; GOST 25584—2016 “Methods for laboratory determination of the filtration coefficient”; GOST 22733—2016 “Soils. Method for laboratory determination of maximum density”; GOST 5180—2015 “Soils. Methods of laboratory determination of physical characteristics”; GOST 25100—2020 “Soils. Classification”. It is shown that the effective strengthening of weak clay soil is achieved as a result of its preliminary stabilization with the help of granulated blast-furnace slag or natural limestone of ≈2.5 mm fraction. The rational amount of granulated blast-furnace slag or limestone is 15 wt.% of the soil mass and at the same time, clay soil has the highest strength value — (2.25–2.45) MPa. The difference in strength indicators in favor of limestone constitutes 9.0%. It has been experimentally established that in order to increase reinforced clay soil strength it is effective to use granulated blast-furnace slag in combination with finely ground blast-furnace slag which rational amount of is 10 wt.% of soil mass which achieved strength of corresponds to M20–M25 grade. It has been defined that for comprehensive improvement of the indicators as strength, density, and frost resistance it is necessary to introduce additionally to clay soil, reinforced with blast-furnace metallurgical slag as reactive components which it’s effective to use Portland cement in amount of not more than 5 wt.% of soil mass in combination with dry complex chemical additive “PRA” which rational amount of constitutes 2.0 wt.% by weight of (Portland cement + finely ground blast-furnace slag). Practical significance: Stabilized and comprehensively strengthened weak clayey soil is characterized by the following actual indicators: M50 F35 K10 — 0.026 m/day which can be used as a base at construction of transport routes of local importance in the regions of the North.

Foamed concrete is mostly used for backfilling of long-distance tunnels and compressive strength is an important technical index to control the quality of foamed concrete. The influence factors on compressive strength of low-density foamed concrete were obtained by the single factor test method based on the targeted dry density and compressive strength. The results show that the HT composed of pollution-free animal protein oil and vegetable oil is an efficient foaming agent and can produce stable foams. The cementation ability of cement can be fully expressed when a water to cement ratio of 0.45~0.5 is employed, making foamed concrete have a compressive strength higher than 2 MPa. The foam content is inversely proportional to the compressive strength and dry density of foamed concrete, and the volume ratio of slurry to foam should be 2:1~3:1. The content of fly ash is also inversely proportional to the compressive strength but positively proportional to the dry density. When the content of admixture is 40~55%, the compressive strength of foamed concrete with low density is not less than 2 MPa. The mixing proportion can be changed in the reasonable range to meet the requirements of different projects.

This is a study on how to reduce shrinkage and improve crack resistance of foamed concrete. By selecting different curing temperatures and humidity, six different curing conditions were analyzed. The shrinkage deformation and maximum crack width of foamed concrete blocks with water–cement ratios of 0.4 and 0.5, under six curing conditions, were measured by a comparator and optical microscope, and the cracking time was recorded. The effects of curing temperature, humidity and water–cement ratio on the shrinkage and crack resistance of the foamed concrete were analyzed by comparing the experimental results of each group. We studied the primary and secondary order of the three factors affecting the drying shrinkage of foamed concrete. The results show that: temperature is the primary factor that changes the drying shrinkage performance of foamed concrete, followed by the water–cement ratio, and finally humidity. The interaction of these three factors is not obvious. The shrinkage of foamed concrete increases with the increase in temperature; increasing the humidity of curing can control the water loss rate of foamed concrete and reduce shrinkage. Lower humidity and higher temperature will make cracks appear earlier; with an increase in the water–cement ratio, the initial cracking time is shortened and the cracking property of foamed concrete is improved.

In this paper, the mechanical properties of perforated steel plate reinforced concrete were studied. Through the compression test of the specimen, the failure mode, the compressive ultimate bearing capacity, and the stress–strain curve of the specimen were obtained. The results show that the compressive strength of perforated steel plate reinforced concrete is twice that of the same grade of plain concrete; through the pull-out test of the specimen, the failure mode and the ultimate uplift bearing capacity were obtained. The finite element software ANSYS was used to simulate the perforated steel plate reinforced concrete specimen, and the results show that the model is reliable. Through the range analysis method, the influence degree of the three factors of the thickness of the perforated steel plate, the hole diameter, and the hole spacing on the compressive strength and the ultimate bearing capacity of the pull-out was studied, and the optimal solution was obtained. The analysis results show that the order of the three factors on the compression and pull-out tests is: the plate thickness of the perforated steel plate > the hole diameter > the hole spacing; the optimal combination of the compressive strength of the perforated steel plate reinforced concrete specimen is that the thickness of the perforated steel plate is 0.75 mm, the diameter of the perforated steel plate is 15 mm, and the spacing of the perforated steel plate is 5 mm; the optimal combination of the ultimate bearing capacity of the pull-out is that the thickness of the steel plate with holes is 1.0 mm, the diameter of the steel plate with holes is 15 mm, and the spacing of the steel plate with holes is 15 mm.