Why is the compiler adding padding to a struct that's already 4-byte aligned?

This issue has been reproduced using multiple 32-bit architectures

I have the following struct in which the sum of all the data member sizes is 76 bytes:

typedef struct
{


    uint32_t unused_32;

    //Unrolled arrays
    uint8_t ar1_1;
    uint8_t ar1_2;

    uint8_t ar2_1;
    uint8_t ar2_2;

    uint8_t ar3_1;
    uint8_t ar3_2;

    uint8_t ar4_1;
    uint8_t ar4_2;
    uint8_t ar4_3;
    uint8_t ar4_4;
    uint8_t ar4_5;
    uint8_t ar4_6;


    uint8_t ex1;
    uint8_t ex2;
    uint8_t ex3;
    uint8_t ex4;
    uint8_t fsi_1;
    uint8_t fsi_2;
    uint8_t fsi_3;
    uint8_t fsi_4;


    uint64_t ex5;
    uint64_t ex6;
    uint64_t Unused_1;
    uint64_t Unused_2;
    uint64_t Unused_3;
    uint64_t Unused_4;

    uint32_t Crc;       

} testStruct;

However, when I do a sizeof() on the struct I get 80 bytes and I'm having trouble figuring out why. When I set the preprocessor to use the "#pragma pack(1)" option and do a sizeof(), it returns 76 bytes, indicating that the compiler is adding padding.

I printed out the addresses of every data member of the structure and everything is in sequential order in memory with no 'holes'. I also added an initialization for a 32-bit integer before the struct and printed out its address, and it came right before the first datamember of the struct, indicating that the padding that's being added is at the end.

76 bytes is already 4-byte aligned, why is the compiler adding an additional 4 bytes onto the end of the struct to make it 80 bytes?