Modular floor tile system with expansion joint

A flooring system including a plurality of modular floor tiles and at least one floor tile expansion joint for use in creating a flooring surface on an underlying surface, the system comprising:

• a plurality of modular floor tiles molded of at least a first polymer, the modular floor tiles including a first modular floor tile and a second modular floor tile, each modular floor tile having a body with a horizontal, substantially planar web with an upper surface and a general lower surface;
• each modular floor tile having a first edge surface that extends from the upper surface of the modular floor tile to the general lower surface of the modular floor tile, and a second edge surface that extends from the upper surface of the modular floor tile to the general lower surface of the modular floor tile, the first edge surface having at least one first connector and the second edge surface having at least one second connector, the first connector of one modular floor tile fastening to a second connector of an adjacent modular floor tile to affix said one modular floor tile to the adjacent modular floor tile;
• the expansion joint including first and second expansion bodies, the first expansion body having a first web with a first general upper surface and a first general lower surface, a plurality of first edge surfaces of the first expansion body including a first outer edge surface, the first edge surfaces extending from the first general upper surface of the first expansion body to the first general lower surface of the first expansion body, the first outer edge surface of the first expansion body including at least one first connector fastened to a second connector of the first modular floor tile, the first expansion body having a first inner margin opposed to the first outer edge surface, at least two spaced-apart first fingers of the first expansion body disposed below the general lower surface of the first expansion body and extending beyond the first inner margin in a first direction in alignment with a predetermined direction of expansion and contraction, each of the first fingers having sides in alignment with the predetermined direction of expansion and contraction, a first channel spacing apart the first fingers and extending below the general lower surface of the first web, sides of the first fingers forming portions of respective sidewalls of the first channel;
• the second expansion body of the expansion joint having a second web with a second general upper surface and a second general lower surface, a plurality of second edge surfaces of the second expansion body extending from the second general upper surface of the second expansion body to the second general lower surface of the second expansion body, the second edge surfaces of the second expansion body including a second outer edge surface, the second outer edge surface of the second expansion body including at least one second connector fastened to a first connector of the second modular floor tile, the second expansion body having a second inner margin opposed to the second outer edge, at least one second finger of the second expansion body disposed below the second general lower surface of the second expansion body and extending beyond the second inner margin in a second direction that is opposite the first direction, sides of the second finger being in alignment with the predetermined direction of expansion and contraction, the second expansion body having at least two second channels disposed beneath the second general lower surface, sides of the said at least one second finger forming portions of respective sidewalls of said least two channels;
• wherein
• the first fingers advance into and retract out of the second channels, and said at least one second finger advances into and retracts out of said at least one first channel, as a function of the temperature of the first and second modular tiles.